To provide a height adjuster of an attached top board, which is capable of easily and surely adjusting the height and especially eliminating any possibility of the top board falling from a furniture body.

This height adjuster for adjusting the height of the attached top board disposed between the facing surfaces of the upper surface of the furniture body 20 and the lower surface of the attached top board disposed thereon, includes operation shafts 41 and 141 and fixed tubes 45, 45' and 145. The fixed tubes are fixed to the furniture body or the attached top board and formed with female threads 46 and 146, while the operation shafts are rotatably supported at the attached top board or the furniture body and formed with male threads 42 and 142, and the male threads are engaged with the female threads with their end parts projecting from the fixed tubes, and the end parts are attached with pull-out prevention members 51 and 151. The operation shafts are rotated to lift/lower the attached top board, and the pull-out prevention members regulate the lifting/lowering height of the attached top board.