Provided is a state monitoring system that monitors a state of an apparatus provided in a wind turbine, including a wireless measuring unit including a sensor provided to the apparatus, and a data collection. The wireless measuring unit includes a memory storing measured data obtained from the sensor, and a wireless communication unit transmitting the measured data obtained from the sensor to the data collection device. When the data collection device has not been able to receive the measured data from the wireless measuring unit, the data collection device requests the wireless measuring unit to retransmit the measured data.