A switch apparatus is provided, including: a main switch connected between first and second terminals, and electrically connecting or disconnecting the first and second terminals according to gate voltage applied to a gate terminal; a voltage output unit having a voltage divider including a first voltage-division resistance on the first terminal side and a second voltage-division resistance on the second terminal side, and outputting voltage corresponding to voltage of the first terminal and voltage of the second terminal if the main switch is caused to enter a connected state; a buffer outputting voltage following output voltage of the voltage output unit in a connected state of the main switch; and a switch control circuit supplying first voltage corresponding to output voltage of the buffer to the gate terminal, and supplying a second voltage corresponding to output voltage of the buffer to a bulk terminal of the main switch.