The power consumption is lowered in an apparatus equipped with memories. Assuming that memories are, for example, of DRAM type, each usage circumstance of DRAM modules on a chip is observed by an observation circuit and a power supply control signal is made to be generated by a CPU in order to turn off the power supply to the DRAM modules actually in a vacant condition, in a disused condition or in an unnecessary condition according to that circumstance observed result. It becomes possible to lower the power consumption as a whole apparatus by turning off only DRAM modules in a disused condition and the like according to the power supply control signal in the power supply on/off circuit.