Abstract: A floor structure of a vehicle body is provided with a floor having a tunnel member disposed in the center of the vehicle body with respect to the width direction of the vehicle body such that it extends in the forward/backward direction of the vehicle body and a floor member disposed adjacent to the tunnel member in the width direction of the vehicle body. The floor member has a joint portion joining to the tunnel member. The floor structure is further provided with a closed section formed at a root portion of the tunnel member by use of the tunnel member and the floor member, and a cross member disposed on the floor member such that it extends in the width direction of the vehicle body. The cross member has a flange portion connected to the tunnel member. Here, the joint portion of the floor member to be joined to the tunnel member overlaps the flange portion of the cross member to be connected to the tunnel member throughout entire of the flange portion.