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A tree generates a complicated stress distribution inside the stem during its formation, which is called 'residual growth stress (RGS)'. The RGS often induces warp in a sawn lumber such as bow, crook, and other deformation, which causes severe losses of materials and benefits in the sawmill industry. Generally, warp becomes more serious in the lumber 'without pith' than in the lumber 'with pith'. In Japan, 50% of conifer plantations are ready to produce large-diameter logs of which diameter is more than 30 cm. The use of those logs inevitably leads to the production of the lumber 'without the pith', so we are concerned about the problems due to lumber warp in future sawmill industry using largediameter logs. Based on those practical background, this study presents a computational procedure to predict warp of the squared lumber, such as a beam, a bearer, and so forth, when those lumbers are sawn from the log and/or the thick plank. Using the derived procedure, 2-D patterns of the RGSs in the sawn lumbers and their changes during sawing processes are simulated. Simulated results will be experimentally verified by measuring the warp of the sawn lumber, as well as by measuring the RGS distributions in a log.