A vehicular device has a device main body, a device box housing the device main body, a terminal block attached to a wall of the device box, and a wire harness electrically connected to the device main body via the terminal block. The terminal block includes an O-ring. The O-ring has a ring-shaped O-ring main body and a lock target portion which is continuous with the O-ring main body. The lock target portion has a connection portion which is continuous with the O-ring main body at one end and a lock target portion main body which is continuous with the other end of the connection portion and projects perpendicularly to an extension direction of the connection portion. The lock target portion main body has a hollow portion in a base portion which is continuous with the other end of the connection portion, and thereby assumes a tubular shape.