To provide a dust-roof/water-proof structure for a linear motion guide with a spring for actualizing smooth operation of the linear motion guide while surely preventing the entry of dust and mud water into the line motion guide.

A linear motion guide unit 50 has bellows cylinder bodies 57, 58 mounted between an upper face 54a of a guide fixing member 54 of the linear motion guide 51 with an elastic member which has a linear motion guide 51A consisting of a rod 52, a leaner bearing 53 and the guide fixing member 54, and a spring member 51B integrated therewith, and a guide supporting member 55 supporting the rod 52 at its upper end, and between a lower face 54b of the guide fixing member 54 and a guide supporting member 56 supporting the rod 52 at its lower end, respectively. The guide fixing member 54 has an air vent hole 59 opening to each of the upper face 54a and the lower face 54b of the guide fixing member 54 to connect a space S1 covered with the upper bellows cylinder body 57 with a space S2 covered with the lower bellows cylinder body 58.