To provide a relay box for a vehicle, arranged without occupying internal space of a cabin and preventing the entry of rainwater, dust, or the like.

The relay box 32 for the vehicle 10 is provided at a vehicle body to store a relay 24. The relay box 32 disposed under the floor of the vehicle body is provided, for the maintenance of the relay 24, with a box side lid 54 at the upper part of the relay box 32; an opening 46b provided in a floor panel 46 of the vehicle body so as to be located above the relay box 32; and a maintenance lid 56 for detachably blocking the opening 46b.