To improve the riding comfort of a person seated in a vehicle by enabling a step space of the person seated in the rear seat arranged on a compartment floor to be widened.

A tunnel 33 bulging out upwardly and extending in a longitudinal direction of a vehicle body 2 is formed halfway in a compartment floor 16 in front of a rear seat 19 and in a width direction of the vehicle body 2. The tunnel 33 is formed in such a manner that a height H at the rear part of the tunnel 33 with a general surface 37 in the compartment floor 16 being applied as a reference line becomes gradually lower as it approaches the rear part and that the rear end upper surface of the tunnel 33 may approach the general surface 37. A recess 42 opened rearward is formed halfway in a width direction at the rear end of the tunnel 33. Reinforcement plates 43 bridging the right and left edges of the recess 42 and connected to them are installed. Rear ends of the reinforcement plates 43 are connected to the mutually connected portions of a front floor panel 23 and a rear floor panel 24.