To measure speed accurately and in a short time according to the situation even if the moving speed of a belt conveyor 1 becomes unstable.

A pulse computation part 5 performs, in parallel, period computation for counting time at which the number of pulses of a pulse signal in proportion to the moving speed of the belt conveyor 1 reaches a reference pulse number and pulse count computation for counting the number of pulses of the pulse signal within reference measurement time. Based on the counted time and the counted pulse number, a frequency computation part 7 computes frequencies in proportion to the moving speed of the belt conveyor 1. A display part 13 displays the speed of the belt conveyor 1 from any of the computed frequencies. While the speed is displayed based on the pulse count computation, when the computed frequency based on the counted time falls within an error range, a switching control part 9 controls the computation part 7 so that a computed frequency is outputted based on the period computation.