It is an object to provide a signal processing circuit for which a complex manufacturing process is not necessary and whose power consumption can be suppressed. In particular, it is an object to provide a signal processing circuit whose power consumption can be suppressed by stopping the power supply for a short time. The signal processing circuit includes a control circuit, an arithmetic unit, and a buffer memory device. The buffer memory device stores data sent from the main memory device or the arithmetic unit in accordance with an instruction from the control unit; the buffer memory device comprises a plurality of memory cells; and the memory cells each include a transistor including an oxide semiconductor in a channel formation region and a memory element to which charge whose amount depends on a value of the data is supplied via the transistor.