PURPOSE: To save energy by eliminating the need for the electric power source of a scaler by providing an electricity generating mechanism which is driven by use of the motion energy of a body to be measured.

CONSTITUTION: By contacting body 1 of revolution to be measured, generator 2 generates an alternating voltage, which is converted 3 from AC to DC before being stored in accumulator 4. This DC voltage is used as electric power sources of logical operation part 5, output part 6, display driving part 7, etc. The output voltage of generator 2 is in proportion to the rotational frequency of body 1 of revolution and waveform-shaped 9 into pulses, which are AND-ed 11 with the output of reference time generator 10 to perform fixed arithmetic 5, making display 8 of a rotational frequency per unit time.