To maintain good appearance of a human body detecting means on a toilet seat device so that a substantially black sensor window, seen from the front of a toilet bowl, is not exposed as much as possible when a toilet seat lid is closed.

The sensor window 9 is disposed opposite to the toilet seat 7 and the toilet stool seat lid with a projection space interposed between them on the front side of a casing 8 substantially vertically so that the human body detecting sensor 1 and the sensor window 9 are of the same level with the back edge of the toilet seat lid 3 or below that. By this arrangement, seen from the front of the toilet seat device body, the most part of the sensor window 9 is hidden below the back edge of the toilet lid 3 so that the substantially black sensor window 9 is hardly seen. Accordingly, the good appearance of the toilet seat device can be maintained.