To provide a linear guide device capable of reducing the installation area.

A guide rail 5 of this linear guide device 1 is provided with guide grooves 55 having a U-shaped cross section opened to the side and positioned in an inside upper surface 53 and an inside lower surface 54. A slide block 7 is provided with ball retaining grooves 74 in an upper surface 72 and a lower surface 73 facing to the guide grooves 55 of the guide rail 5 and the both ends are connected via the inside passage 75 so as to be formed with circulating passages 76. A linear guide 78 is so formed that, multiple balls 77 retained by a ball retainer groove 74 roll along the guide grooves 55, while respective balls 77 circulating in the circulating passage 76 so that the slide block 7 is freely slidingly supported to the inner side upper surface 53 and the inner side lower surface 54 of the guide rail. The linear guide 78 is so formed that one hemispherical surface 80 of each ball 77 is retained by the ball retainer groove 74 and the other hemispherical surface 79 are supported to the guide groove 55.