A heating and hot water supplying device includes: a circulation passage that connects a heat exchanger and an external heating terminal; a bypass passage that bypasses the heating terminal by branching from the circulation passage; a hot water supply passage for supplying the hot water heated to a preset hot water supply temperature by the heat exchanger for hot water supply; a control unit that controls operations in which this plurality of units are used; and an operation terminal for performing various operations. A distribution valve is provided in the branching portion of the bypass passage. The distribution valve adjusts the distribution ratio so that each of a heating operation, a hot water supplying operation, and a simultaneous heating and hot water supplying operation is possible. The operation terminal is provided with a prohibit switch to prohibit the simultaneous heating and hot water supplying operation.