An information collection system includes a plurality of radio tags and a reading device. Each of the radio tags stores identification information and includes a sensor, an antenna that receives a carrier wave from the reading device, and a data transmission unit that sends measurement data including the identification information and information obtained by the sensor to the reading device after the carrier wave is received by the antenna. The plurality of radio tags send the identification information and the information obtained by the sensor with different natural periods from the data transmission units. The reading device transmits the carrier wave to each of the radio tags, receives data from each of the radio tags, and obtains the data.