A recording current optimization method to optimize a recording current according to a change of a driving voltage applied to a pre-amplifier that generates the recording current supplied to a head, a recording medium storing a program that executes the method, and an apparatus that employs the method. The headwear piece has a crown defining an opening through which a wearer’s head can project with the headwear piece in an operative position on the wearer’s head. The torque detection module generates an actual torque signal of a transmission.