An electromagnetic wave oscillation device includes: a buck-boost circuit having buck-boosters and switching elements; an electromagnetic wave oscillator; an amplifier to amplify an electromagnetic wave and supply an amplified electromagnetic wave to a resistive part; a detector to detect a reflected wave from the resistive part; and a controller to send to one of the switching elements an operation signal in predetermined order, synchronizing with an oscillation timing of the electromagnetic wave oscillator, to output a current from the corresponding buck-boosters to the amplifier in a non-smooth manner. When a detected value of the reflected wave exceeds a predetermined value upon said current output by operating the one of the switching elements, the controller stops sending the operation signal to one or more of the other switching elements that are supposed to output the current after said current output by operating the one of the switching elements.