A lie-down massager includes a base frame having an elongated top panel, through which an elongated top opening is formed centrally and lengthwise, a rider provided below the elongated top panel of the base frame, a guide member movably engaged between the base frame and the rider so as to enable the rider to make a horizontally reciprocal movement relative to the base frame, massage bumps that move vertically and/or horizontally along the elongated top opening of the elongated top panel of the base frame, and a lifter that holds the massage bumps and adjusts the height of the massage bumps. The lifter includes two vertical screws that rotates together by a chain and two nuts engaging with the screws so that rotating the screws lift or lower the nuts thereby adjusting the height of the massage bumps. A motor rotates the screws via a worm gear.