PURPOSE: To make the measurement of a set time possible in the form of an actually used time by deciding whether a load is consuming power or not and measuring the time only when the load is used.

CONSTITUTION: Upon turning a start switch 5a ON, a measurable state is brought about in the timer section 5 which outputs a control signal. When a load switch 6 is subsequently turned ON to bring about the usable state of a load 7, the timer section 5 measures the time interval when the load 7 is in the usable state based on a signal representative of the using state of the load 7 detected at a detecting section 3. When the use of the load 7 is stopped for a predetermined time, the measurement of time is stopped during that time interval. When the timer section 5 is in the measurable state, a control section 4 feeds power based on the control signal therefor and when a set using time of the load 7 is reached and the timer section 5 enters into a measurement waiting state, power supply is interrupted. Since the set time matches the actually used time, power is not interrupted independently from the using time of the load 7.