PURPOSE: To reduce power consumption in an arithmetic section by allowing the arithmetic section to count an integration signal from an integration section and selecting an interrupt signal generating section by a changeover means when no count pulse exists.

CONSTITUTION: A changeover switch 1 is thrown to the position of an integration section 2 and an interrupt signal generating section 4 and a count section 6 sends a count pulse signal A to the integration section 2 normally. The integration section 2 integrates the count pulse signal A from the changeover switch 1 for a prescribed time and outputs an integration signal B to an arithmetic section 3. The arithmetic section 3 receives the signal B from the integration section 2 to read the integration value and outputs a switching signal D to the changeover switch 1. An interrupt signal generating section 4 outputs an interrupt signal C to the arithmetic section 3 when the section 4 receives one count pulse signal A from the changeover switch 1 thrown by the switching signal D after lapse of a prescribed time. A counter 6 outputs a count pulse based on a measurement object to operate a display section 7.