A capacitor unit includes a casing, a heat sink, a heat radiation sheet, and a notch. The casing accommodates the capacitors. The casing includes a positive electrode terminal block and a negative electrode terminal block. The heat sink is provided on the casing in a stacking direction. The heat radiation sheet is made of insulation material and is sandwiched in the stacking direction between the casing and the heat sink to cover the positive electrode terminal block and the negative electrode terminal block. The notch is provided in at least one of the casing and the heat radiation sheet between the negative electrode terminal block and the positive electrode terminal block. The notch passes through the at least one of the casing and the heat radiation sheet along a plain substantially perpendicular to the stacking direction to separate the negative electrode terminal block and the positive electrode terminal block.