Abstract: A power supply device includes an oscillator configured to output an alternating-current (AC) signal in accordance with strength of an external force, a rectifying output unit configured to convert the AC signal to a first signal which is a pulsating current, a rectifying-smoothing output unit configured to convert the AC signal to a second signal which is closer to a direct current than the first signal is, a starter unit configured to output a start-up signal, and a controller starting up in response to the start-up signal. The starter unit includes a first terminal electrically connected to the rectifying output unit, and a second terminal electrically connected to the rectifying-smoothing output unit. The starter unit outputs the start-up signal when a voltage applied to the first terminal is equal to or higher than a voltage applied to the second terminal. The power supply device reliably starts up the controller.