A plunging type constant velocity universal joint for a rear-wheel drive shaft, comprising: an outer joint member having a cylindrical inner peripheral surface in which eight track grooves extending in an axial direction of the plunging type constant velocity universal joint are formed; an inner joint member having a spherical outer peripheral surface in which eight track grooves extending in the axial direction are formed, and having a spline hole formed along an axial center of the inner joint member ; eight balls arranged in ball tracks formed by the track grooves of the outer joint member and the track grooves of the inner joint member ; and a cage , which has eight pockets configured to receive the balls , and is held in slide contact with the inner peripheral surface of the outer joint member and the outer peripheral surface of the inner joint member , wherein a curvature center of a spherical portion formed on an outer peripheral surface of the cage and a curvature center of a spherical portion formed on an inner peripheral surface of the cage are offset to opposite sides in the axial direction with respect to a joint center (O(s)) by an equal distance, characterized in that the plunging type constant velocity universal joint has a maximum operating angle of 20° or less, a ratio PCD BALL /D BALL of a pitch circle diameter PCD BALL of the balls to a diameter D BALL of each of the balls is set from 3.3 to 3.6, a ratio T I /D BALL of a radial thickness T I of the inner joint member to the diameter D BALL of each of the balls is set from 0.30 to 0.45, a ratio PCD SPL /D BALL of a pitch circle diameter PCD SPL of the spline hole of the inner joint member to the diameter D BALL of each of the balls is set from 1.70 to 1.85, and a ratio W I /D BALL of an axial width W I of the inner joint member to the diameter D BALL of each of the balls is set from 1.2 to 1.55. an outer joint member having a cylindrical inner peripheral surface in which eight track grooves extending in an axial direction of the plunging type constant velocity universal joint are formed; an inner joint member having a spherical outer peripheral surface in which eight track grooves extending in the axial direction are formed, and having a spline hole formed along an axial center of the inner joint member ; eight balls arranged in ball tracks formed by the track grooves of the outer joint member and the track grooves of the inner joint member ; and a cage , which has eight pockets configured to receive the balls , and is held in slide contact with the inner peripheral surface of the outer joint member and the outer peripheral surface of the inner joint member , wherein a curvature center of a spherical portion formed on an outer peripheral surface of the cage and a curvature center of a spherical portion formed on an inner peripheral surface of the cage are offset to opposite sides in the axial direction with respect to a joint center (O(s)) by an equal distance, characterized in that the plunging type constant velocity universal joint has a maximum operating angle of 20° or less, a ratio PCD BALL /D BALL of a pitch circle diameter PCD BALL of the balls to a diameter D BALL of each of the balls is set from 3.3 to 3.6, a ratio T I /D BALL of a radial thickness T I of the inner joint member to the diameter D BALL of each of the balls is set from 0.30 to 0.45, a ratio PCD SPL /D BALL of a pitch circle diameter PCD SPL of the spline hole of the inner joint member to the diameter D BALL of each of the balls is set from 1.70 to 1.85, and a ratio W I /D BALL of an axial width W I of the inner joint member to the diameter D BALL of each of the balls is set from 1.2 to 1.55. <EOS>