To provide a toilet bowl device that allows the toilet seat to be opened and closed without any trouble and to remain self-supporting in an open position and allows the backrest to be installed in a correct position suited for use.

A toilet seat 24 is bisected to right and left halves, the halves 24L and 24R are assembled upward and downward and rightward and leftward openably to a toilet bowl body 12 through hinges 34, and a backrest 16 is provided upward the toilet bowl body 12.