To provide a rack-and-pinion type hydraulic power steering system that helps a reduction in weight and cost of its sealing structure for pressure oil without causing accuracy deterioration and breakage of component parts and leakage of pressure oil.

A cylindrical member 20 made of synthetic resin, which is inserted into a housing 5 surrounding a rack 4 meshing with a pinion, is prevented from moving inward in the housing 5 because of its own contact with a step on the inner periphery of the housing 5 through a metallic reception member 24 integrated with itself. The rack 4 is prevented, on the other, from moving in one axial direction because of its own contact with the cylindrical member 20 through its movement checking part 6. The outer periphery of the rack 4 and the inner periphery of the cylindrical member 20 hold therebetween a sealing member 21 that is pressed into the cylindrical member 20, and the sealing member 21 is encircled by a cylindrical metallic reinforcing member 26 that is integrated with the cylindrical member 20. This cylindrical member 20 defines in the housing 5 further inward an oil chamber 13 for a hydraulic cylinder for steering assist force generation.