A control device has: an external terminal receiving a control signal; an output setting circuit changing an output state every time a predetermined edge appears in the control signal; an oscillator generating a clock signal; a period detector counting the number of pulses in the clock signal to detect whether or not the control signal has been kept at a predetermined logic level for a predetermined period; an initializing circuit initializing, based on the output of the period detector, the output state specified by the output setting circuit when the control signal is found to have been kept at the predetermined logic level for the predetermined period; and an oscillation control circuit permitting the operation of the oscillator only when the control signal is at the predetermined logic level and inhibiting the operation of the oscillator otherwise.