Provided is a parameter derivation method for deriving a parameter for a wireless power transmission system that transmits power from a power transmission device to a power receiving device via electric field coupling, the parameter including a coupling coefficient ke for an electric field coupling unit constituted by an active electrode and a passive electrode in a power transmission device and a power receiving device. The coupling coefficient (ke) is derived on the basis of a prescribed operational expression by using resonance frequencies omega1, omega2 or anti-resonance frequencies omega00, omega0 of an input impedance that were measured in a state where the active electrode and the passive electrode of the power receiving device are open, and resonance frequency omega r or anti-resonance frequency omega a of the input impedance that were measured in a state where the active electrode and the passive electrode of the power receiving device are short-circuited. Thereby, provided is a practical method for deriving a parameter closer to an actual state in a wireless power transmission system that transmits power from a power transmission device to a power receiving device via electric field coupling.