PURPOSE: To improve buckling strength, impact strength and bending strength by making an inner surface cross-section which is perpendicular with the axial line at least, in one part of a tube, pentagonal or polygonal having more angles than the former.

CONSTITUTION: This fiber-reinforced synthetic resin tube 1 has an outer diameter becoming smaller in one direction of an axial line, and the synthetic resin used is an epoxy resin or phenol resin, and the reinforcing fiber used is carbon fiber or glass fiber. The inner surface cross-section which is perpendicular with the axial line in one part of the tube is pentagonal or polygonal having more angles than the former. The degree of a diametral reduction of the outer diameter in one direction of the axial line should preferably be 6/1000 to 7/1000. In addition, the length of an area A should preferably be 4 to 20% of the length of the tube (length of a shaft from the viewpoint of practical use), especially 5 to 13%. Further, the inner surface cross-section at the terminal part side 1b (an area B) in a larger diameter of the tube should preferably be pentagonal or polygonal having more angles than the former. The length of the area B should preferably be 4 to 30% of the length of the shaft from the viewpoint of practical use.