PURPOSE: To perform quick and accurate measurement, by obtaining the time required until n-times before at every time when n detecting objects installed in the peripheral area of a disk concentrically fitted to the vertical shaft of a gyro, pass a prescribed location.

CONSTITUTION: Plural sections to be detected, for example, a disk 10 having slits 14W17 for a photo sensor, are fitted to the vertical shaft 5 of a gyro. The pulse of a pulse generator 20 is inputted into an FF22 and an AND circuit 32. The signal from slits 14W17 is also inputted into the AND circuit 32 thugh a waveform shaping circuit 26 and D-type FFs 28 and 30. At every time when the slits generate pulses, the AND circuit 32 produces a latch pulse, and a latch circuit 34 calculates the counting value of the time, and then, an operating section 36 calculates the period between the pulses and stores them in R1WR4 of a register 38. The oldest pulse is successively replaced with new one and correct times of one period are always, measured. In this way, the charging is stabilized and the precise measurement of time can be started, and thus, the quick-response and high-accuracy measurement can be performed.