A simulation program was developed which calculates fractured volume of granite from relation between temperature rise and loss in strength of granite. Simulation was carried out up to 2000 kW output power and 60 minute duration time. Results are as follows: (1)Temperature rise after microwave radiation increases with increase of radiation power and duration time. Temperature rises higher by higher radiation power than longer duration time in the case of same radiation energy (power × duration time). (2)Fractured volume increases with increase of radiation power and duration time. The volume is larger in the case of higher radiation power than longer duration time at the same radiation energy.