A wireless power supply apparatus using magnetic resonance is provided for a linear motion type robot. In the apparatus, a high-frequency signal for foreign matter detection is generated. This signal is different in wavelength and frequency from a high-frequency signal for transmitting power between a power transmission coil and a power reception coil. The wavelength is wavelength λ and the frequency is frequency f. The power transmission coil serves as an apparent antenna of which the long side is set to λ/2. At least either of a wavelength λx or a resonance frequency fx of a resonance wave attributed to the resonance in the antenna is detected when the high-frequency signal is supplied to the antenna. Whether or not foreign matter is present on the power transmission coil is detected based on the wavelength λx or the resonance frequency fx.