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 to form a raceway of the ball , and both of the raceway grooves 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 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 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 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 ; characterized in that a distal end surface of the tongue unit 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 (R) 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 to form a raceway of the ball , and both of the raceway grooves 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 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 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 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 ; characterized in that a distal end surface of the tongue unit 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 (R) 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 . <EOS>