Thermal cracking due to heat of cement hydration has been a problem for　especially large scale structures as grabity dams. Recently as large scale structures such as tanks, caissons, and substructures for bridges are constructed, thermalcracking becomes a serious problem for these structures. Thermal cracking is caused by restraint to volume change of concrete. Therefore to make clear the mechanism of the restraint is indispensable for control of cracking.
　As to straight wall members, some predictive methods for the restraint to volume change have been suggested. However research data on the thermal cracking in cylindrical members is insufficient. Hence, the authors studied the thermal cracking in cylindrical members through model tests and numerical analysis using finite element method.
　As a result of the model tests and the numerical analysis, the degree of restraint for cylindrical members tended to be rather smaller than that for straight walls. It is considered to be caused by reduction of tensile stress due to out-plane　displacement of cylindrical walls.