A linear motion guiding device comprising: a guide rail; a slider; and a plurality of balls, wherein the slider is provided at an outside of the guide rail; the guide rail and the slider face with each other and respectively include, at mutually facing positions, a raceway groove (11, 12, 211, 212) to form a raceway of the ball, and both of the raceway grooves (11, 12) extend in a longer direction of the guide rail; the slider includes a slider main body and a pair of end caps; via the ball rolling within the raceway in a load state, the slider linearly moves along the guide rail; the raceway groove (11, 12, 211, 212) and a return path of the ball are formed to the slider main body, and a direction changing passage of the ball is formed to the end cap; the ball is provided in a circulation pathway including the raceway, the return path, and the direction changing passage; an arc groove (221, 222, 511, 512, 521, 522) configured to form an outer peripheral surface of the direction changing passage is formed to a surface of a side of the slider main body of the end cap; and a tongue unit (25, 511a, 512a, 521a, 522a) configured to scoop up the ball from the raceway and guide the ball to the direction changing passage is formed to an end of a side of the raceway of the arc groove (25, 511a, 512a, 521a, 522a); characterized in that a distal end surface of the tongue unit (25, 511a, 512a, 521a, 522a) includes a plane perpendicular to a direction along the raceway and a circular-arc surface configured to cave into an arc shape from the plane; in that a curvature radius of the circular-arc surface is smaller than a radius of the ball; and in that a center (Os) of a circle indicating a curvature of the circular-arc surface is present on a line shifted from a groove bottom line (Lm) of the arc groove by at least an offset amount between the raceway groove of a side of the guide rail and the raceway groove of a side of the slider. a guide rail; a slider; and a plurality of balls, wherein the slider is provided at an outside of the guide rail; the guide rail and the slider face with each other and respectively include, at mutually facing positions, a raceway groove (11, 12, 211, 212) to form a raceway of the ball, and both of the raceway grooves (11, 12) extend in a longer direction of the guide rail; the slider includes a slider main body and a pair of end caps; via the ball rolling within the raceway in a load state, the slider linearly moves along the guide rail; the raceway groove (11, 12, 211, 212) and a return path of the ball are formed to the slider main body, and a direction changing passage of the ball is formed to the end cap; the ball is provided in a circulation pathway including the raceway, the return path, and the direction changing passage; an arc groove (221, 222, 511, 512, 521, 522) configured to form an outer peripheral surface of the direction changing passage is formed to a surface of a side of the slider main body of the end cap; and a tongue unit (25, 511a, 512a, 521a, 522a) configured to scoop up the ball from the raceway and guide the ball to the direction changing passage is formed to an end of a side of the raceway of the arc groove (25, 511a, 512a, 521a, 522a); characterized in that a distal end surface of the tongue unit (25, 511a, 512a, 521a, 522a) includes a plane perpendicular to a direction along the raceway and a circular-arc surface configured to cave into an arc shape from the plane; in that a curvature radius of the circular-arc surface is smaller than a radius of the ball; and in that a center (Os) of a circle indicating a curvature of the circular-arc surface is present on a line shifted from a groove bottom line (Lm) of the arc groove by at least an offset amount between the raceway groove of a side of the guide rail and the raceway groove of a side of the slider.