A control method for a power transmitting device is provided, the power transmitting device including a power transmitting antenna, which transmits AC power wirelessly to the power receiving antenna of a power receiving device, and an oscillator. The method includes supplying pulse signals that control first and second switching element groups to the oscillator, and changing a phase shift amount between a first pulse signal and a second pulse signal. The method also includes causing the oscillator to change the voltage of the AC power output and to set an initial value of the phase shift amount. The method further includes causing the oscillator to output preliminary AC power of a voltage to reduce the phase shift amount from the initial value, fixing the phase shift amount, and causing the oscillator to output the AC power while maintaining the voltage corresponding to the fixed phase shift amount.