A state output circuit that outputs a state signal indicating a state of a power supply apparatus, including: a state output terminal that outputs the state signal; a reference potential line to which a reference potential is applied; a first pull-up terminal to which a first pull-up potential is applied, wherein the first pull-up potential is a potential higher than the reference potential; a connection switch unit that is provided between the state output terminal and the reference potential line, and switches whether to connect the state output terminal to the reference potential line or not, in accordance with the state of the power supply apparatus; a first protection resistor provided between the connection switch unit and the state output terminal; and a pull-up unit that pulls up a first connection line between the first protection resistor and the connection switch unit up to the first pull-up potential.