A wheel condition-monitoring system comprises transmitters (1) installed on individual rotatable wheels, for transmitting conditions of the wheels, and a receiver (11) installed on the side of a vehicle body, for receiving the conditions of the wheels sent from the transmitters. The rotation speed of the wheels are detected, and data that indicate the conditions of the wheels are sent from the transmitters (1) to the receiver (11) at intervals in accordance with the rotation speeds detected, or data that relate to a pressure etc. are sent for a predetermined number of times at a transmission interval of a first cycle that assumes a high speed range. At the same time, data transmission of a predetermined number of times corresponding to the transmission interval of the first cycle is repeated for a predetermined number of times at a transmission interval of a second cycle that assumes a low speed range and is longer than the first cycle. This increases reliability in data transmission and reception, and enables the system to function stably in the presence of a dead point.