PURPOSE: To improve the working efficiency of assembling various kinds of parts inside the body by providing a removable upper back panel connected between a pair of suspension towers in the cross direction of a vehicle in a module assembly structure in which an upper module and an under module of a car body are assembled.

CONSTITUTION: A car body 10 is divided into an upper module 16 for forming the periphery of a roof 12 and the periphery of a door opening 14 and an under module UNDRM 20 for forming an under body, and the dividing positions of the respective modules are closed section portions. A tire house 30 is formed on both sides portions of the rear side of a vehicle of the UNDRM 20, and an upper back panel 34 is stretched between suspension towers 32 formed on the upper end portion of the tire house 30. In this arrangement, projecting portions 42 projected below the vehicle are formed on both end portions in the width direction of the upper back panel 34, and engaged with recess portions 44 formed on the suspension towers 32. After that, both the suspension towers 32 and the upper back panel 34 are removably connected to each other by bolts 50 and nuts 52.