Upon power-on, a microprocessor is reset and initiates a cold start initialization program stored in ROM for initializing the microprocessor and associated peripherals. Thereafter, externally input control signals to the microprocessor indicate a desirable initialization operation for a warm start when the microprocessor is subsequently reset by an operator. A reset address generating circuit generates (1) a first address setting signal to set a first starting address of the initialization program for a cold start when receiving the reset signal at a power-ON or (2) a second address setting signal to set a second starting address of the initialization program corresponding to the warm start after the power-ON when receiving both a reset signal and a control signal generated externally by a user. A program counter is then set to an address corresponding to the inputted address setting signal. The microprocessor reads and executes initialization programs based on instructions in memory addressed by the program counter.