To provide a moulded body having a specific cross-sectional structure that can prevent a defect of sink marks from generating on a design surface of the moulded body corresponding to rib parts, has a small thickness and a large size, and can achieve sufficient strength and rigidity. A moulded body 1 having a specific cross-sectional structure includes a rib part 3 standing on a back surface 2b opposite to a design surface 2a of a main body 2 of the moulded body 1. A reduced thickness part 4 is formed on the back surface 2b of the main body 2 at both sides or one side of the rib part 3, the ratio D/T is 0.975 to 1.07 where D is the diameter of a circle that passes through base ends 3b of both side faces 3a of the rib part 3 and is in contact with the design surface 2a of the main body 2 positioned between the base ends 3b, and T is the thickness of the main body 2 at an outer side of the reduced thickness part 4, and t < 1.3(T - n) is satisfied where t is the thickness of the rib part 3, and n is the thickness of the reduced thickness part 4.