An immobilizer receiver for an outboard motor includes a control unit that is housed in a liquid-tight case and arranged to receive an authentication code, an antenna wire arranged to receive the authentication code, and an answer-back buzzer arranged to provide an indication that the authentication code has been received, which are housed in a recessed section of a housing. A distance from an opening surface to a bottom surface of the recessed section of the housing is arranged such that the antenna wire can receive the authentication code even in a case that a hull is made of metal. Then, the opening surface of the housing is preferably mounted on a vertical or approximately vertical surface of the hull. Therefore, it is possible to secure a receiving function of the antenna wire that is housed on the bottom surface of the recessed section. In addition, the answer-back buzzer is protected against coming in contact with water. The immobilizer receiver can easily be mounted to a hull and has a receiving function that is secured.