A hot-water supply unit, comprising: a housing; a tank disposed within the housing, and configured to store water; a heating mechanism disposed within a machine space which is formed by the housing therein, and configured to heat up the water stored in the tank; and an electric component unit disposed within the machine space, and having a plurality of electric components configured to operate at least a part of the heating mechanism; wherein: the housing includes a removable side plate which covers at least a part of the machine space; the heating mechanism is positioned rearward of the electric component unit with respect to the removable side plate; the electric component unit has a lower component box accommodating at least one of the electric components, and an upper component box accommodating at least another of the electric components; and the upper component box is configured to be switched between a first state of being positioned on the lower component box within the housing and a second state of being positioned outside of the housing, characterized in that: the heating mechanism is positioned above the tank; the hot-water supply unit further comprises a thermal insulator positioned at a lower inside of the housing, a main frame disposed within the machine space to support the heating mechanism and the electric component unit substantially within the main frame, and a support plate disposed between the thermal insulator and the main frame and supporting the main frame with respect to the thermal insulator; the upper component box is attached to the main frame in a detachable manner; and the housing is configured such that at least a part of the upper component box in the first state is exposed to outside of the housing when the removable side plate is removed. a housing; a tank disposed within the housing, and configured to store water; a heating mechanism disposed within a machine space which is formed by the housing therein, and configured to heat up the water stored in the tank; and an electric component unit disposed within the machine space, and having a plurality of electric components configured to operate at least a part of the heating mechanism; wherein: the housing includes a removable side plate which covers at least a part of the machine space; the heating mechanism is positioned rearward of the electric component unit with respect to the removable side plate; the electric component unit has a lower component box accommodating at least one of the electric components, and an upper component box accommodating at least another of the electric components; and the upper component box is configured to be switched between a first state of being positioned on the lower component box within the housing and a second state of being positioned outside of the housing, the housing includes a removable side plate which covers at least a part of the machine space; the heating mechanism is positioned rearward of the electric component unit with respect to the removable side plate; the electric component unit has a lower component box accommodating at least one of the electric components, and an upper component box accommodating at least another of the electric components; and the upper component box is configured to be switched between a first state of being positioned on the lower component box within the housing and a second state of being positioned outside of the housing, characterized in that: the heating mechanism is positioned above the tank; the hot-water supply unit further comprises a thermal insulator positioned at a lower inside of the housing, a main frame disposed within the machine space to support the heating mechanism and the electric component unit substantially within the main frame, and a support plate disposed between the thermal insulator and the main frame and supporting the main frame with respect to the thermal insulator; the upper component box is attached to the main frame in a detachable manner; and the housing is configured such that at least a part of the upper component box in the first state is exposed to outside of the housing when the removable side plate is removed. the heating mechanism is positioned above the tank; the hot-water supply unit further comprises a thermal insulator positioned at a lower inside of the housing, a main frame disposed within the machine space to support the heating mechanism and the electric component unit substantially within the main frame, and a support plate disposed between the thermal insulator and the main frame and supporting the main frame with respect to the thermal insulator; a thermal insulator positioned at a lower inside of the housing, a main frame disposed within the machine space to support the heating mechanism and the electric component unit substantially within the main frame, and a support plate disposed between the thermal insulator and the main frame and supporting the main frame with respect to the thermal insulator; the upper component box is attached to the main frame in a detachable manner; and the housing is configured such that at least a part of the upper component box in the first state is exposed to outside of the housing when the removable side plate is removed.