PURPOSE: To enable a starting time to be, exactly measured, by indicating the starting time of a motor with a numerical value.

CONSTITUTION: From a start trigger circuit 3, by first FG signal among the FG signals of output generated from a frequency generator, the output of start signal is generated. By a counter 4, the counting of clock pulse is started when the start signal is applied to. In the meantime, by an F/V converter, the FG signal is F/V-converted. From a window comparator 2, the output of pulse is generated every time output signal from the F/V converter 1 coincides with an upper limit value or a lower limit value. By a latch circuit 6, the counting value of the counter 4 is latched every time the output of the pulse is generated from the window comparator 2, and is indicated on an indicator 7. As a result, a starting time can be exactly measured.