PURPOSE: To execute rate measurement even in the case of such an electronic timepiece as a rate shift of a wide range is generated by detecting a leakage flux of the electronic timepiece and converting it to an electric signal.

CONSTITUTION: Magnetic flux data detected by a sensor 1 is amplified by an amplifier 2, and binarized by a window comparator 3. With respect to an obtained output, only head rise data is extracted by a mask circuit 4, and by a pulse encoded by a code detecting circuit 5, an output of a free-running counter 6 is stored in a storage circuit A 7 together with code data. Also, by an output of a reference clock, the output of the counter 6 is stored in a storage circuit B 8, a detection timing value of the magnetic flux data stored in the circuit A 7, and an output timing count value of the reference clock stored in the circuit B 8 are read out by a CPU 9, and a rate is calculated from a change with the lapse of time of its difference. At that time, by calculating the data of the same codes, the rate measurement over a wide range can be executed.