A signal processing circuit whose power consumption can be suppressed is provided. In a period during which a power supply voltage is not supplied to a storage element, data stored in a first storage circuit corresponding to a nonvolatile memory can be held by a first capacitor provided in a second storage circuit. With the use of a transistor in which a channel is formed in an oxide semiconductor layer, a signal held in the first capacitor is held for a long time. The storage element can accordingly hold the stored content (data) also in a period during which the supply of the power supply voltage is stopped. A signal held by the first capacitor can be converted into the one corresponding to the state (the on state or off state) of the second transistor and read from the second storage circuit. Consequently, an original signal can be accurately read.