PURPOSE: To make the operation of setting time simple by displaying the carry by one of the contents having been displayed till then in an electrochromic display (ECD) at the exchanging of batteries.

CONSTITUTION: When a new battery is charged, the display content of an ECD 8 is fed through a detecting circuit 9 to a decision circuit 11 and an encoder circuit 10. The output of the circuit 10 is fed to a clock counter 12, and when it is decided 11 that the display of the ECD 8 exists actually, the counter 12 is preset by the output of a power-on-reset circuit 1. The minute counter of the counter 12 is counted by +1 by the output of a one-shot circuit 6.