CONTACTLESS POWER TRANSMISSION SYSTEM FOR TRANSMITTING POWER FROM POWER TRANSMITTER APPARATUS TO POWER RECEIVER APPARATUS, AND DETECTING FOREIGN OBJECT

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