Patent ID: 8707778

Claim:
A transmission device provided in a tire cavity area to transmit tire information about a condition of a tire, the transmission device comprising: a sensor configured to detect, as the tire information, a condition of gas filled in the tire cavity area surrounded with the tire and a rim; a transmitter configured to wirelessly transmits the detected tire information; and a housing which houses the sensor and the transmitter, the housing including a protruding portion protruding in a protruding direction from a surface of the housing, the protruding portion including a top portion defining an opening portion of an air vent connecting an inner space of the housing and the tire cavity area, the opening portion having an area of 0.4 mm 2 or smaller, a height of the protruding portion being 1 mm or greater, and an area of a contact portion between the top portion and a contact plane that is in contact with the top portion and perpendicular to a protruding direction of the protruding portion is not larger than 30% of the area of the opening portion.