A foreign object detection sensor applied to an electric sliding door apparatus is provided. The sensor includes a contact detecting section, a change detecting section, and a determination section. The contact detection section has a pressure sensitive portion which is capable of elastically changing in form through contact with a foreign object. The contact detecting section outputs a contact detection signal. The change detecting section measures the time required for the oscillation signal for a predetermined number of cycles to be outputted within a measurement period, which is set shorter than the response time it takes from when the object makes contact with the pressure sensitive portion to when the contact detecting section outputs the contact detection signal in the case where the movable body is in the closing operation at a predetermined maximum moving speed.