A transmitter module has a sensor module that includes a plurality of sensors and operates intermittently, a signal processor module that permits transmission of an output of the sensor module to a receiver module at given permission timings, a radio transmission module that wirelessly transmits data when the transmission is permitted, and a power source that supplies power to each module. The signal processor module has a microcomputer and an interval timer that outputs a first timing signal when a count value corresponds to a set value. The microcomputer is activated by the first timing signal and changes the set value in a compare register according to a vehicle operation state.