CONTACTLESS ELECTRICITY SUPPLY DEVICE

contactless electric power supply device 100 to charge a battery 28 of a vehicle includes a power transmitting circuit 101 having a power transmitting coil 12 and a charging circuit 201 having a power receiving coil 22. An electric power is transmitted from power transmitting coil 12 to power receiving coil 22 in a contactless manner. When the vehicle approaches power supply device 100, a trial power supply in which a electric power transmission through a minute electric power is carried out is executed and a power transmission efficiency from power transmitting coil 12 to power receiving coil 22 is estimated on a basis of a current flowing through power transmitting circuit 101. From this power transmission efficiency, a determination of whether power receiving coil 22 falls in a range in which battery 28 is chargeable with respect to power transmitting coil 12 is made.