To provide a detection method of detecting a decentering degree of a semiconductor wafer placed on a rotating table without requiring a high-level mechanism and high-level sequence control.

A detection method comprises: preparing a device having a rotating table TAB on which a wafer WFR is placed and capable of being rotated, and a sensor SSR capable of detecting a position of an arbitrary target TGT; adjusting a position of the sensor SSR such that an outgoing part radiating energy lines from the sensor SSR for detecting a position of the target TGT, a position distant from an outermost periphery of the wafer WFR placed without decentering with respect to the rotating table TAB by an acceptable amount of decentering, and a position of the target TGT lie in a straight line; placing the wafer WFR on the rotating table TAB; and detecting existence or non-existence of reflection from the wafer WFR, of the energy lines radiated from the outgoing part while rotating the rotating table TAB on which the wafer WFR is placed thereby to detect existence or non-existence of decentering of the wafer WFR with respect to the rotating table.