The present invention relates to a foreign object detecting method, and a device and system therefor. A method for detecting a foreign object in a wireless power transmitter according to an embodiment of the present invention may comprise the steps of: when an object placed in a charging area is sensed, measuring quality factor values within an operating frequency band to find a measured peak frequency at which the maximum quality factor value is measured; storing the measured peak frequency and the measured quality factor value corresponding to the measured peak frequency; transmitting information on the type of transmitter to an identified wireless power receiver; receiving a reference quality factor value and a reference peak frequency corresponding to the type of transmitter; calculating a measured inductance by using the measured peak frequency; calculating a reference inductance by using the reference peak frequency; and detecting a foreign object by using at least one of the reference quality factor value, the reference peak frequency, and the reference inductance.