Patent ID: 8760278

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 to which the tire is mounted; a transmitter configured to wirelessly transmit the detected tire information; a housing which includes a wall surrounding the sensor and the transmitter; an inner member provided in the housing; an inner space that is divided from the tire cavity area by the wall and an inner wall of the inner member, and that a sensor face of the sensor faces; and an air vent that passes through the housing and connects the inner space and the tire cavity area, the air vent having an outer opening portion that is formed on an outer surface of the housing facing the tire cavity area and an inner opening portion that is formed on a surface of the housing facing the inner space, the outer opening portion having an opening area of 0.4 mm 2 or smaller, the inner opening portion having an opening area larger than that of the outer opening portion, and a hole cross-sectional area of the air vent increasing in a stepwise fashion or continuously from the outer opening portion toward the inner opening portion.