A toilet seat device 9 comprises a toilet seat 5, a casing 2 provided to the rear of the toilet seat 5, and a functional component that sprays a liquid or discharges or sucks in a gas. The functionalcomponent is, for example: a private-parts washing device 61 that washes the private-parts of a seated person; an air blowing device 62 that blows warm air to the inside of a toilet bowl; or a deodorizing device 63 that deodorizes the inside of the toilet bowl. At least a portion of the functional component is installed in the toilet seat 5, and the remaining portion of the functional component isinstalled in the casing 2.