PURPOSE: To provide a protective circuit capable of evading the generation of clock interruption clue to the malfunction of a CPU for a CPU clock selective supply circuit for selectively supplying the clock signals of plural systems to the CPU based on a command from the CPU.

CONSTITUTION: This circuit is provided at least one of an erroneous selection protective circuit 21 for changing a selection command sel so as to select the present clock signal and supplying it to a selection control register 15 when the selection command sel supplied from the CPU 10 based on the combination of flags FLG1 and FLG2 for indicating the presence of the clock signals CK1 and CK2 is going to select the absent clock signal as a CPU clock and an erroneous stoppage protective circuit 22 for changing an ON/OFF command so as to continue an operation and supplying it to ON/OFF control registers 14a and 14b when ON/OFF control signals en1 and en2 supplied from the CPU based on the selection command SEL held in the selection control register 15 are going to stop the operation of clock supply circuits 11 and 12 outputting the clock signal under selection.