A millimeter waveband switch which enables high isolation without increasing passing loss, includes a first switching element that is connected in series between input and output terminals through which a signal passes; and a first transmission line having an electrical length of ½ wavelength and which is connected in parallel with the first switching element. Alternatively, the millimeter waveband switch may include: a first switching element having a first end connected in parallel to input and output terminals through which a signal passes; a first transmission line having an electrical length of ½ wavelength which is connected in parallel with the first switching element; and a second transmission line having an electrical length of ¼ wavelength and which is connected between aground and a second end of her first switching element.