A transfer mechanism is used for transferring a target object having a mainly circular contour. The transfer mechanism includes a transfer unit that supplies movements in angular and rectilinear directions to a pick for supporting the target object. An optical sensor is disposed at a standby position on a route of the target object toward a destination, to optically detect presence/absence of the target object on the pick. Angular and rectilinear misalignment amounts of the target object in the angular and rectilinear directions are calculated, with reference to detection and reference values of a signal output from the optical sensor, and at least one of detection and reference values of a radius of the target object. A controller controls the transfer unit to compensate for the angular and rectilinear misalignment amounts in transfer of the target object by the pick.