To provide a sensor apparatus for automatic doors having less labor for installation.

At one end section of the door frame 2 at a side where the automatic door 1 is in contact in closing, a light source 6 and a light receiver 7 are provided. By two mirrors 9a and 9b that are arranged in the automatic door 1, light that is emitted from the light source 6 is guided to the light receiver 7 to form a light path 11 nearly in a U shape. An operation opening 3 that opens to the front side of the automatic door 1 is provided between the light source 6 and the mirror 9a for forming so that the light path 11 crosses the inside of the operation opening 3. The light source 6, the light receiver 7, the light path 11, and the operation opening 3 are arranged compactly while they are close one another, thus installing the sensor apparatus for automatic doors with less labor.