A position alignment of a transfer point of a transfer arm is performed by using a position detecting wafer capable of being loaded into an apparatus having a thin transfer port. The position detecting wafer S includes an electrostatic capacitance detecting sensor 50 for detecting an electrostatic capacitance in relation with a reference object for the position alignment. The electrostatic capacitance detecting sensor 50 includes a plurality of electrostatic capacitance detecting electrodes 52, each forming the electrostatic capacitance in relation with the reference object; and a control circuit 51 for controlling a detection of the electrostatic capacitance by each electrostatic capacitance detecting electrode 52, while communicating with each electrostatic capacitance detecting electrode 52. The electrostatic capacitance detecting electrodes 52 are provided on a rear surface of the position detecting wafer S, and the control circuit 51 is provided on a front surface of the position detecting wafer S.