A method for driving a contactless power transmission device including a setting surface, which includes a power supplying area, and a primary side circuit, which is located in the power supplying area and formed by a primary coil and a capacitor, wherein when an electric instrument, the electric instrument including a secondary side circuit formed by a secondary coil and a resonance capacitor (Cx), is set in the power supplying area, the contactless power transmission device excites the primary coil located in the power supplying area and produces electromagnetic induction at the secondary coil to supply power to the electric instrument, the method comprising: exciting the primary coil selectively using a first frequency, which is a frequency determined by the primary coil and the capacitor located in the primary side circuit, wherein the secondary coil is not excited by power supplied from the primary side circuit, when the primary coil is excited selectively at the first frequency; setting a second resonance frequency to a resonance frequency that excites the primary coil and resonates the secondary side circuit of the electric instrument when the electric instrument is being placed in the power supplying area, wherein the output of the primary coil relative to the frequency in the secondary side circuit of the instrument becomes maximum at the second resonance frequency; and exciting the primary coil selectively using the second resonance frequency, wherein the exciting of the primary coil includes: exciting the primary coil at the first frequency to detect metal or the electric instrument and determine whether or not metal exists in the power supplying area based on a primary current that flows to the primary coil, suspending excitation of the primary coil at the first frequency and the second resonance frequency when determined that the metal exists in the power supplying area or that nothing exists in the power supplying area, exciting the primary coil at the second resonance frequency to detect the electric instrument when determined that an object other than the metal exists in the power supplying area and determine whether or not the object existing in the power supplying area is the electric instrument based on the primary current, and exciting the primary coil at the second resonance frequency and supplying power to the electric instrument when determined that the object is the electric instrument. exciting the primary coil selectively using a first frequency, which is a frequency determined by the primary coil and the capacitor located in the primary side circuit, wherein the secondary coil is not excited by power supplied from the primary side circuit, when the primary coil is excited selectively at the first frequency; setting a second resonance frequency to a resonance frequency that excites the primary coil and resonates the secondary side circuit of the electric instrument when the electric instrument is being placed in the power supplying area, wherein the output of the primary coil relative to the frequency in the secondary side circuit of the instrument becomes maximum at the second resonance frequency; and exciting the primary coil selectively using the second resonance frequency, wherein the exciting of the primary coil includes: exciting the primary coil at the first frequency to detect metal or the electric instrument and determine whether or not metal exists in the power supplying area based on a primary current that flows to the primary coil, suspending excitation of the primary coil at the first frequency and the second resonance frequency when determined that the metal exists in the power supplying area or that nothing exists in the power supplying area, exciting the primary coil at the second resonance frequency to detect the electric instrument when determined that an object other than the metal exists in the power supplying area and determine whether or not the object existing in the power supplying area is the electric instrument based on the primary current, and exciting the primary coil at the second resonance frequency and supplying power to the electric instrument when determined that the object is the electric instrument. exciting the primary coil at the first frequency to detect metal or the electric instrument and determine whether or not metal exists in the power supplying area based on a primary current that flows to the primary coil, suspending excitation of the primary coil at the first frequency and the second resonance frequency when determined that the metal exists in the power supplying area or that nothing exists in the power supplying area, exciting the primary coil at the second resonance frequency to detect the electric instrument when determined that an object other than the metal exists in the power supplying area and determine whether or not the object existing in the power supplying area is the electric instrument based on the primary current, and exciting the primary coil at the second resonance frequency and supplying power to the electric instrument when determined that the object is the electric instrument.