PURPOSE: To eliminate the need of an operation time display meter required before in an equipment with a built-in microcomputer.

CONSTITUTION: A function for measuring the time only when respective circuits 3 inside the equipment are operated and the function for displaying the cumulative operation time at a display element by the operation of an equipment user are provided in the microcomputer 2. When a power source switch 1 is turned on, the microcomputer 2 operates the respective circuits 3 inside the equipment and simultaneously starts measuring the cumulative operation time by the above-mentioned function. Also, since the microcomputer 2 is connected to the display element 5 as well, the cumulative operation time can be displayed at the element 5 by the operation of the equipment user. Thus, the operation time display device of the microcomputer applied equipment can be simply constituted at a low cost.