An electronic timepiece is provided with a device for automatically adjusting month-end calendar dates capable of reading dates simply, quickly, and reliably. A date detection pattern 71 composed of reflective and non-reflective sections is formed on the rear surface of a date dial 70. When the date dial 70 rotates, a change in the boundary between the reflective part and the non-reflective part is read by a photo sensor 81, the necessary number of dates is determined by a control circuit 20 by use of a perpetual calendar circuit, driving a date dial driving mechanisms 51 and 52.