To provide a vehicle body lower part structure enhancing strength against a load applied to a front face of a vehicle and securing a desired cabin space when applying the load to the front face.

In this vehicle body lower part structure 11, a reinforcing member 91 is mounted in a groove of a U-shape in cross section in a floor frame 17 included in a floor of a cabin. In the reinforcing member 91, a second groove bottom side 114 of a second reinforcing member 96 of a groove shape is arranged along a first groove bottom side 106 of a first reinforcing member 95 of a groove shape. A first projecting bead part 115 of a projecting shape in cross section projected in a direction separate from the second groove bottom side 114 is formed on the first groove bottom side 106. A second projecting bead part 126 of a projecting shape in cross section projected in a direction separate from the first groove bottom side 106 is formed on the second groove bottom side 114. A closed section shape is formed by the first/second projecting bead parts 115 and 126.

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