A power supply control device, comprising: a power reception terminal for receiving power; a power supply terminal for supplying power; a relay configured to make and break an electrical connection between the power reception terminal and the power supply terminal; a control circuit configured to control the relay; characterized by further comprising a power supply circuit configured to supply power to the control circuit by use of power received via the power reception terminal; and a printed wiring board, wherein the control circuit and the power supply circuit are mounted on the printed wiring board, wherein the power supply control device further comprises: an electrical circuit electrically connecting the power reception terminal and the power supply terminal; and a block holding the power reception terminal, the power supply terminal, the relay, the printed wiring board, and the electrical circuit, wherein: the relay is configured to make and break the electrical connection between the power reception terminal and the power supply terminal by opening and closing the electrical circuit; the block has a first end and a second end respectively defining opposite ends in a first direction, and a third end and a fourth end respectively defining opposite ends in a second direction perpendicular to the first direction; the power reception terminal and the power supply terminal are positioned at the first end and the second end, respectively; the electrical circuit is positioned closer to the fourth end than the third end such that a circuit accommodating space is formed closer to the third end than the fourth end; and the control circuit and the power supply circuit are positioned in the circuit accommodating space. a power reception terminal for receiving power; a power supply terminal for supplying power; a relay configured to make and break an electrical connection between the power reception terminal and the power supply terminal; a control circuit configured to control the relay; characterized by further comprising a power supply circuit configured to supply power to the control circuit by use of power received via the power reception terminal; and a printed wiring board, wherein the control circuit and the power supply circuit are mounted on the printed wiring board, an electrical circuit electrically connecting the power reception terminal and the power supply terminal; and a block holding the power reception terminal, the power supply terminal, the relay, the printed wiring board, and the electrical circuit, wherein: the relay is configured to make and break the electrical connection between the power reception terminal and the power supply terminal by opening and closing the electrical circuit; the block has a first end and a second end respectively defining opposite ends in a first direction, and a third end and a fourth end respectively defining opposite ends in a second direction perpendicular to the first direction; the power reception terminal and the power supply terminal are positioned at the first end and the second end, respectively; the electrical circuit is positioned closer to the fourth end than the third end such that a circuit accommodating space is formed closer to the third end than the fourth end; and the control circuit and the power supply circuit are positioned in the circuit accommodating space. the relay is configured to make and break the electrical connection between the power reception terminal and the power supply terminal by opening and closing the electrical circuit; the block has a first end and a second end respectively defining opposite ends in a first direction, and a third end and a fourth end respectively defining opposite ends in a second direction perpendicular to the first direction; the power reception terminal and the power supply terminal are positioned at the first end and the second end, respectively; the electrical circuit is positioned closer to the fourth end than the third end such that a circuit accommodating space is formed closer to the third end than the fourth end; and the control circuit and the power supply circuit are positioned in the circuit accommodating space.