A mounting and dismounting device for a toilet seat and a toilet lid comprising: a pin and a pin case for mounting and dismounting; the pin and the pin having a rod portion and a head portion protruding from a tip of the rod portion further toward the outside than an outer peripheral surface of the rod portion, wherein the pin case includes an insertion section having an insertion hole into which the pin is inserted, a passage section having a head passage space which communicates with the insertion hole and allows the head portion of the pin inserted into the insertion hole to move in a direction orthogonal to a longitudinal direction of the insertion hole, and a holding section having a rod disposition space which communicates with the insertion hole and the head passage space and in which the rod portion is to be disposed, the holding section holding the rod portion in the rod disposition space by opening and closing an opening and closing port between the rod disposition space and the insertion hole, and in a case where the rod portion is held in the rod disposition space, an end portion on the head passage space side of the holding section fastens the head portion such that the pin does not come out from the pin case, characterized in that the shape of the insertion hole is a cylindrical shape, and the diameter of the insertion hole is larger than the outer diameter of the head portion, and the height H1 of the insertion hole is less than or equal to the length of the rod portion, the insertion hole has an insertion opening in a lower surface of the pin case, and when mounted, the lower surface F1 side of the mounting and dismounting device 6 is placed on the upper end face of the toilet bowl, the insertion hole extending toward the upper side of the pin case from the insertion opening, and is connected to the head passage space of the passage section, to allow insertion of the pin: into the insertion hole from the head portion side of the pin to the rod portion side of the pin. a pin and a pin case for mounting and dismounting; the pin and the pin having a rod portion and a head portion protruding from a tip of the rod portion further toward the outside than an outer peripheral surface of the rod portion, wherein the pin case includes an insertion section having an insertion hole into which the pin is inserted, a passage section having a head passage space which communicates with the insertion hole and allows the head portion of the pin inserted into the insertion hole to move in a direction orthogonal to a longitudinal direction of the insertion hole, and a holding section having a rod disposition space which communicates with the insertion hole and the head passage space and in which the rod portion is to be disposed, the holding section holding the rod portion in the rod disposition space by opening and closing an opening and closing port between the rod disposition space and the insertion hole, and in a case where the rod portion is held in the rod disposition space, an end portion on the head passage space side of the holding section fastens the head portion such that the pin does not come out from the pin case, characterized in that the shape of the insertion hole is a cylindrical shape, and the diameter of the insertion hole is larger than the outer diameter of the head portion, and the height H1 of the insertion hole is less than or equal to the length of the rod portion, the insertion hole has an insertion opening in a lower surface of the pin case, and when mounted, the lower surface F1 side of the mounting and dismounting device 6 is placed on the upper end face of the toilet bowl, the insertion hole extending toward the upper side of the pin case from the insertion opening, and is connected to the head passage space of the passage section, to allow insertion of the pin: into the insertion hole from the head portion side of the pin to the rod portion side of the pin.