An electrical circuit is provided in a casing. The electrical circuit includes a capacitor having a particular function needed for realizing the electrical circuit. The electrical circuit includes an electrical component configured to generate heat due to energization. A flow creator creates, in the casing, an air flow that flows in a direction from the electrical component to the capacitor such that air heated by heat generation of the electrical component flows to the capacitor. A controller controls the flow creator. The capacitor has a characteristic that capacitance monotonically decreases or monotonically increases as temperature rises, in a part of a temperature range in which the electrical circuit operates. The controller detects a capacitance change due to a temperature change of the capacitor caused by the air heated by the heat generation, and controls the flow creator based on a detection result of the capacitance change.