To provide a warming structure warming hot water in a bathtub fully by electric power obtained by drainage, keeping the bathtub hygienic for a long time, and facilitating an addition of various functions to the bathtub.

The warming structure includes a power generation means connected to a drain of the bathtub for storing hot water, a power storage means for storing electric power generated by the power generation means, and a heater disposed at the bathtub. When hot water in the bathtub is drained from the drain, the power generation means generates electric power so as to be stored in the power storage means, and when hot water is stored in the bathtub, the electric power stored in the power storage means is supplied to the heater to warm the hot water in the bathtub. The power generation means is operated so as to store the generated electric power in the power storage means by a control means, and the electric power stored in the power storage means is supplied to various loads including the heater by the control means.