For example, the first controller 117 of the wireless power transmitting device 110 may calculate power of the wireless power transmitting device 110 based on signal values measured at V1_sense and I1_sense of FIG. 5A or 5B and transmit a power value regarding the calculated power to the wireless power receiving device 120. In addition, the second controller 127 of the wireless power receiving device 120 may calculate power of the wireless power receiving device 120 based on signal values measured at V2 sense and I2 sense of FIG. 5A or 5B and transmit a power value regarding the calculated power to the wireless power transmitting device 110.

In this example, the wireless power transmitting device 110 or the wireless power receiving device 120 may calculate the wireless power efficiency using the power value measured by themselves and the power value received from the counterpart to obtain the calculated wireless power efficiency. For example, the calculated value of the wireless power efficiency may be maximized and/or improved in a situation where the position of the wireless power transmitting device 110 and the position of the wireless power receiving device 120 are aligned with each other.