The present invention relates to a wireless power transmitting device. The wireless power transmitting device comprises a transmitter coil section with a plurality of partially overlapping transmitter coils; a fan for cooling heat generated by the transmitter coil section; and a controller for sending out a detection signal through the transmitter coil section, calculating the number of operating coils based on the strength of a response signal to the detection signal, and controlling the fan based on the calculated number of operating coils. Accordingly, heat generated by the transmitter coils can be reduced more efficiently.