PURPOSE: To enable simple and quick calculation of a speed by detecting a time lag between the corresponding characteristic points of waveforms detected by two sensors disposed at a prescribed interval in the direction of movement.

CONSTITUTION: A speed meter is constructed of two sensors 11a and 11b disposed longitudinally in the direction of movement, filters 13a and 13b extracting signals of specific frequencies from the respective outputs of the sensors, a counter 18 detecting a phase difference between the two extracted signals, and ROM 19 converting the phase difference into a speed. The specific frequencies are set so that a phase delay of one period or longer does not occur between the two signals at the lowest speed in the sphere of measurement. By this constitution, the signals of the frequencies causing no phase delay of one period or longer at the lowest speed in the sphere of measurement are extracted 13a, 13b from detection outputs from the two sensors 11a and 11b disposed longitudinally in the direction of movement, the phase difference between the waveforms of the two signals is determined by the counter 18, and the speed is determined from the phase difference by the ROM 19. Thereby calculation of the speed is enabled only by detecting the time of lag between characteristic points.