CONTACTLESS POWER TRANSMISSION SYSTEM

A detector (13) detects a value of a current or voltage generated by an auxiliary coil (L3). A detector (14) detects a value of a current flowing through a power transmitting coil (L1). A coupling coefficient estimator (15) estimates a first coupling coefficient (k12a) between the power transmitting coil (L1) and a power receiving coil (L2), based on the value of the current or voltage generated by the auxiliary coil (L3), and estimates a second coupling coefficient (k12b) between the power transmitting coil (L1) and the power receiving coil (L2), based on the value of the current flowing through the power transmitting coil (L1). A control circuit (16) controls a power supply circuit to stop power transmission to a power receiver apparatus (20) when a difference between the coupling coefficients is greater than a threshold.