According to one embodiment, a toilet seat apparatus that includes a main part mounted at a rear upper part of a toilet, a toilet seat provided rotatably with respect to the main part, and a radio wave sensor being provided in the interior of the main part and using a radio wave to sense a human body; and in the state in which the toilet seat is lowered, the toilet seat covers the radio wave sensor, and the radio wave passes through the toilet seat and is radiated frontward of the radio wave sensor.