PURPOSE: To make it unnecessary to provide an operation start control circuit for controlling an operation start of an internal control circuit, as an external circuit, and also, to suppress a delay time to the operation start of the internal control circuit to the absolute minimum, in the case of constituting a system by using plural microprocessors formed by containing a clock generating circuit.

CONSTITUTION: After a power source is turned on or after it is reset, whether an internal generation clock is stabilized by synchronizing with a reference clock or not is monitored, and until the internal generation clock is stabilized by synchronizing with the reference clock, an nMOS transistor 44 is turned on, and in the case the internal generation clock is stabilized by synchronizing with the reference clock, the nMOS transistor 44 is turned off, and also, in the case an external terminal 36 becomes a high level from a low level, inhibition of an operation start to an internal control circuit 43 of an operation start control circuit 48 is released.