To provide a main frame of a vehicle for construction/civil engineering work such as a hydraulic shovel and a bulldozer, which can enlarge the inner width dimension of the main frame in simple structure without enlarging the all-over width dimension of the vehicle, make it possible to mount a variety of on-vehicle equipment with ease, and in addition, lighten with the mounting strength and rigidity of mounting members to the main frame secured and reduce the cost of products and working cost substantially.

A continuous carrying-in space (A) in which a variety of on-vehicle equipment do not interfere with each other is secured by setting mounting sections on which various mounting members 11 and 15 fixed to a part of the inside face of a frame body 1a are mounted in minimum essential size, and fixing the mounting sections on which the members 11 and 15 are mounted to the fixing sections 16 and 18 integrally by shaving off the inside face of the mounting sections on which the mounting members 11 and 15 are mounted and the inside face of the fixing sections 16 and 18 of the frame body 1a as much as possible to prevent various on-vehicle equipment from interfering with each other. This constitution makes it possible to set the inner width dimension of the frame body 1a in large size without increasing the outer width dimension and also reduce the weight of the main frame 1.