According to an embodiment, a wireless power transmitting device may include a transmission coil, a DC/DC converter configured to output a driving voltage, an inverter configured to output AC power to the transmission coil, and a controller. The controller may be configured to output a first control signal for generating the AC power having a first frequency to the inverter, measure a demodulated voltage generated by demodulating a signal applied to the transmission coil, and output, to the inverter, a second control signal for generating the AC power having a second frequency different from the first frequency, based on a first peak-to-peak value identified in the demodulated voltage being a preset first value or more. The inverter may output the AC power having the second frequency to the transmission coil based on the second control signal. Other various embodiments are possible as well.