A generator (20) is connected in parallel with a bypass circuit (31) and a capacitor (22) for storing electric energy from the generator, and the bypass circuit (31) includes a switch (33) that is controlled to turn on and off depending on the voltage across the capacitor (22). Since the input current to the capacitor decreases, the capacitor voltage becomes low, thus preventing overcharge. The waveform of the generated power corresponds to the cycle of the generator rotation, and the rotation of the generator is controlled accurately according to the waveform so that the accurate time indication can be achieved.