The present invention relates to an easy and cost effective process for extruding a tube having different intermediate sections in its longitudinal direction, and a die for forming a tube through this extrusion molding process. Tubes so formed may be used for a vehicle for example, particularly for the body frame of a motorcycle. The die for this extrusion molding process includes a fixed die and a movable variable die. The tube is formed by material extruded from an outflow passage which is formed by the superposition in the direction of extrusion of a fixed die hole and a variable die hole. The outflow passage has an opening for a tube wall for forming the wall of the tube, and openings for two intermediate walls for forming connecting walls in the inside space of the tube. The tube formed by this process is composed of a part having the connecting wall and a part having no connecting wall. This is accomplished by opening or blocking the opening for the intermediate wall by moving cores according to the amount of the movement of the variable die. The resulting tube has a rigidity that varies along the longitudinal direction of the tube.