A massage device for a massage chair or massage back cushion is provided. The massage device includes: a receiving casing with two sides each provided with an S-shaped track, wherein a rack is disposed at the receiving casing a vertically movable casing adapted to mesh with the rack and forced to move along the rack and a swing casing having a top pivotally coupled to the vertically movable casing, having a bottom connected to the vertically movable casing through at least an elastic component, and being flanked by two rollers rolling along the S-shaped tracks. Two massage balls which mesh with gear trains driven by a power source are disposed on the swing casing. The two massage balls each include a rotating disk and two swing arms. The swing casing and massage balls are guided by the S-shaped tracks in feeding or withdrawing along Z-axis and the human back profile.
