According to one embodiment, a switch includes a first element with a first withstand voltage, a second element whose withstand voltage is lower than the first withstand voltage, a diode which is connected between a positive electrode of the first element and a positive electrode of the second element in such a manner that a direction from the positive electrode of the second element toward the positive electrode of the first element is a forward direction and whose withstand voltage is equal to the first withstand voltage, a negative electrode of the first element and a negative electrode of the second element being connected, and a circuit configured to apply a positive voltage to the positive terminal output a pulse lower than the first withstand voltage when the first element goes off.