To enhance obstacle detection in a defined region such as an elevator car door way or the like by providing a detector for detecting energy beams discharged from a plurality of emitters, and a means for determining the very weak states of the beams discharged from the plurality of emitters.

An emitter array 25 is installed in a first door 20, and a detector array 30 is installed in a second door 15. A controller 35 is installed in the uppermost part of an elevator car 10, and electrically connected to both of the emitter array 25 and the detector array 30. An electrical link 55 functions such that the controller 35 operates the emitter array 25 and the detector array 30 in cooperation with each other. The controller 35 is operated by a very weak beam detecting method, and determines whether an energy beam 40 is very weak or not for the individual pair of the emitter array 25 and the detector array 30.