Devices, compilers and methods to reduce energy consumption associated with execution of a program by adjusting a computational capability of a CPU with higher accuracy than before. A device sets an appropriate computational capability to the CPU. It includes: changing a computational capability of the CPU every time each of a plurality of program areas included in the execution program is executed while the execution program is being executed, and measuring execution time each of the program areas; deciding an optimal computational capability required to execute the program area using the CPU, based on the execution time for each of the computational capabilities measured for the respective program areas; and performing setting of the optimal computational capability for executing the program area, which is to be used when executing the program area again in the course of executing the execution program, for each of the program areas.