To suggest a microwave visible sensor capable of visually detecting the electromagnetic field distribution and the standing wave position of microwaves in a waveguide.

The microwave visible sensor 50 is constituted by: providing a plurality of small holes 36 along a tube axis on the side 34E of an applicator 34 of rectangular waveguide structure; fixing a substrate 38 with a plurality of detection members 37 having antennas 39 suited to each interval of the small holes 36 to the side 34E of the applicator 34; and providing each detection member 37 with a detection diode 40 which is conducted by electromotive force to be generated in the antennas 39, and an LED 41 which is lit by conduction of the detection diode 40.