Power transmitting device and power transfer system

A power transfer system including a power receiving device that has a secondary coil provided at a vehicle and a power transmitting device that contactlessly transmits electric power to the secondary coil, the power transmitting device comprising:

• a plurality of primary coils located separate from the vehicle and arranged at an interval in an arrangement direction;
• a selecting unit configured to select one of the primary coils, to which electric power is to be supplied from a power supply;
• and
• a control unit configured to control the selecting unit, the control unit being configured to cause the power supply to supply the selected primary coil with a second electric power smaller than a first electric power, the control unit being configured to select a power transmitting coil from among the plurality of primary coils based on the basis of at least one of a power transmitting situation of the selected primary coil and a power receiving situation of the secondary coil, the control unit being configured to cause the power supply to supply the power transmitting coil with the first electric power.