Operability, low noise characteristic and endurance are further improved at a reduced cost and easily by suppressing the fluctuation of a pitch between rolling elements due to the effects of swelling caused by oil and fats such as lubricants also in a case of using the elastomer for the material of the retaining piece. In a linear guide device in which a retaining piece 100 made of an elastomeric material is interposed between each of steel balls B adjacent with each other in the circulating direction, the concaved surface 101 of the retaining piece 100 is in contact with the steel ball B adjacent with the retaining piece 100 at a position for 50% or less of the diameter of the steel ball B, and the rigidity value of the retaining piece 100 is defined at 0.053 N/m or more and 0.175 N/m or less.