A holding circuit includes first to third input terminals, an output terminal, first to third switches, a capacitor, and a node. The first to third switches control conduction between the node and the first input terminal, conduction between the node and the output terminal, and conduction between the second input terminal and the output terminal, respectively. First and second terminals of the capacitor are electrically connected to the node and the third input terminal, respectively. The first to third switches are each a transistor comprising an oxide semiconductor layer comprising a semiconductor region. Owing to the structure, a potential change of the node in an electrically floating state can be suppressed; thus, the holding circuit can retain its state for a long time. The holding circuit can be used as a memory circuit for backup of a sequential circuit, for example.
