An underframe structure of a railcar capable of reducing a deformation amount of a cross beam supporting an underfloor equipment upon underfloor fire. The underframe structure of the railcar includes an underframe having a pair of side sills extending in a railcar longitudinal direction and a cross beam arranged between the side sills and extending in a railcar width direction, a structural floor provided on an upper surface of the underframe, and an underfloor equipment suspended down in a center part in the railcar width direction of the cross beam. The underframe structure includes a passenger cabin floor provided on an upper side of the structural floor, the passenger cabin floor forming a lower surface of a passenger cabin S, and floor receiving members supporting the passenger cabin floor and extending in the railcar longitudinal direction between the structural floor and the passenger cabin floor.