To readily and surely confirm lighting of a light-emitting diode, both under cloudy sky and under direct sun in the light-emitting diode provided on one side surface of a relay box.

In a relay box 4 for use in constructing a solar power generation system, to which a roofing 2 obtained by integrating a plurality of solar battery modules M is electrically connected, a solar battery system is provided with a light-emitting diode 11 on one side surface of the relay box 4 and an eave 19 for shading from direct sun of the light-emitting diode in the relay box 4, and the relay box 4 for use in construction of such the solar battery system is provided.