Door structure of a vehicle and method of forming same

An impact bar 16 includes a U-shaped portion 17 which is formed by a vertical face portion 16A and upper-and-lower lateral surface portions 16B, 16C at its front end. The impact bar 16 further includes upper and lower outer-surface portions 16H, 16G. A pair of first connecting portions 16d, 16e which are formed such that they extend from respective front ends of the upper-and-lower lateral surface portions 16B, 16C, up and down, is connected to a lateral surface portion 3e of the door inner panel. 3 A pair of second connecting portions 16H, 16J, which are formed so that they extend from respective front ends of the upper-and-lower outer surface portions 16H, 16G to the front, is connected to a longitudinal surface portion 3f of the door inner panel. 3