PURPOSE: To dispense with a terminal used exclusively for testing by a system wherein a plurality of outside-operated switches employed for ordinary operation are operated simultaneously for setting a test mode.

CONSTITUTION: An output of a quartz oscillator circuit 1 is frequency-divided by a frequency divider circuit 2 and inputted sequentially to a time counter 3 and a calender counter 4. Outputs of the counters 3 and 4 are decoded by decoders 5 and 6 respectively and given to a driving circuit 7, and a display unit 8 is driven by this driving circuit 7. A modification control circuit 19 is connected with a calender modification mode specifying switch terminal 9, a time modification mode specifying switch terminal 10, a forward movement modification switch terminal 11 and a backward movement modification switch terminal 12. When the terminals 9 and 10 are set at a logical value "1" simultaneously, a test mode is set by an output of a detector circuit 20, and the display unit 8 is all lighted.