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Full list of authors: Enya, Keigo; Kobayashi, Masanori; Kimura, Jun; Araki, Hiroshi; Namiki, Noriyuki; Noda, Hirotomo; Kashima, Shingo; Oshigami, Shoko; Ishibashi, Ko; Yamawaki, T.; Tohara, Kazuyuki; Saito, Yoshifumi; Ozaki, Masanobu; Mizuno, Takahide; Kamata, Shunichi; Matsumoto, Koji; Sasaki, Sho; Kuramoto, Kiyoshi; Sato, Yuki; Yokozawa, Takeshi; Numata, Tsutomu; Mizumoto, Satoko; Mizuno, Hiroyuki; Nagamine, Kenta; Sawamura, Akihiko; Tanimoto, Kazuo; Imai, Hisato; Nakagawa, Hiroyuki; Kirino, Okiharu; Green, David; Fujii, Masayuki; Iwamura, Satoru; Fujishiro, Naofumi; Matsumoto, Yoshiaki; Lingenauber, Kay; Kallenbach, Reinald; Althaus, Christian; Behnke, Thomas; Binger, Jan; Daurskikh, Anna; Eisenmenger, Henri; Heer, Ulrich; Hüttig, Christian; Lara, Luisa M.; Lichopoj, Alexander; Lötzke, Horst-Georg; Lüdicke, Fabian; Michaelis, Harald; Pablo Rodriguez Garcia, Juan; Rösner, Kerstin; Stark, Alexander; Steinbrügge, Gregor; Thabaut, Pascal; Thomas, Nicolas; del Togno, Simone; Wahl, Daniel; Wendler, Belinda; Wickhusen, Kai; Willner, Konrad; Hussmann, Hauke.--This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/ by-nc-nd/4.0/)., The Jupiter Icy Moons Explorer (JUICE) is a science mission led by the European Space Agency, being developed for launch in 2023. The Ganymede Laser Altimeter (GALA) is an instrument onboard JUICE, whose main scientific goals are to understand ice tectonics based on topographic data, the subsurface structure by measuring tidal response, and small-scale roughness and albedo of the surface. In addition, from the perspective of astrobiology, it is imperative to study the subsurface ocean scientifically. The development of GALA has proceeded through an international collaboration between Germany (the lead), Japan, Switzerland, and Spain. Within this framework, the Japanese team (GALA-J) is responsible for developing three receiver modules: the Backend Optics (BEO), the Focal Plane Assembly (FPA), and the Analog Electronics Module (AEM). Like the German team, GALA-J also developed software to simulate the performance of the entire GALA system (performance model). In July 2020, the Proto-Flight Models of BEO, FPA, and AEM were delivered from Japan to Germany. This paper presents an overview of JUICE/GALA and its scientific objectives and describes the instrumentation, mainly focusing on Japan's contribution. © 2021 COSPAR., NSO/Kitt Peak data (synoptic maps of He I Å intensity) used here are produced cooperatively by NSF/NOAO, NASA/GSFC, and NOAA/SEL. Sunspot number (version 2) comes from the Sunspot Index and Long-term Solar Observations at Royal Observatory of Belgium, Brussels. All used data are courtesy to be downloaded from their web sites. The authors would like to express their deep thanks to the staffs of these web sites. This work is supported by the National Natural Science Foundation of China (11973085, 11903077, 11803086, and 11633008), the Yunnan Ten-Thousand Talents Plan (the Yunling-Scholar Project), the national project for large scale scientific facilities (2019YFA0405001), and the Chinese Academy of Sciences., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.