A wireless power transfer system is disclosed. A wireless power transmitting apparatus for wirelessly transmitting power to a wireless power receiving apparatus includes a transmitting coil for transmitting the power, a hall sensor for sensing a change width of flux density caused y the wireless power receiving apparatus, and a controller for comparing the sensed change width of the flux density with a predetermined critical value to determine whether to transmit the power, wherein magnets provided in the wireless power transmitting apparatus and the wireless power receiving apparatus are disposed such that polarities of the magnets are different from each other at opposite faces thereof. In the wireless power transfer system, the magnets having polarities are disposed in the wireless power transmitting apparatus and the wireless power receiving apparatus. Consequently, the wireless power transmitting apparatus more effectively senses the change width of the flux density to wirelessly transfer power to the wireless power receiving apparatus.