Transmission device for transmitting tire information and tire information monitoring system

A tire information monitoring system comprising:

• a transmission device including:
• a sensor configured to detect, as tire information, a condition of gas filled in a tire cavity area surrounded with a tire and a rim to which the tire is mounted,
• a transmitter configured to wirelessly transmits the detected tire information, and
• a housing which includes a wall surrounding the sensor and the transmitter, such that an inner space is divided from the tire cavity area by the wall, and an air vent passes through the housing and connects the inner space and the tire cavity area, such that an outer opening portion of the air vent formed on a surface of the housing facing the tire cavity area has an opening area of 0.4 mm2 or smaller, and an inner opening portion of the air vent formed on a surface of the housing facing the inner space has an opening area larger than that of the outer opening portion;
• a receiving device configured to receive the tire information transmitted from the transmitter;
• and
• a monitoring section configured to determine whether a tire anomaly exists based on the tire information and provide a determination result.