The number of elderly people who undergo lumbar fusion surgery (LFS) has been increasing. Postoperative rehabilitation for them can be problematic due to lumbar stiffness. This is the first case report describing exercise therapy using the lumbar-type hybrid assistive limb (HAL) after multiple LFS in an elderly patient. An 83-year-old man underwent LFS at L4-S1. Additional fusion surgery at L2-3 for adjacent segment disease was performed 2 years after the primary surgery. Although the patient's leg pain declined, he had severe locomotive dysfunction at 3 months after his final surgery. He started exercise therapy using the lumbar-type HAL including sit-to-stand training and squat training 4 months after his final surgery. He performed 3 sets of 20 sit-to-stand and 20 squat repetitions with adequate rests in between sets. The HAL training was safely conducted every day for 12 weeks without adverse event. Timed up and go test (TUG), 1-minute sit to stand test (1MSTS), one-leg stand test (OLST), and Berg balance scale (BBS) were assessed as locomotive function measurement. Before HAL therapy, TUG, 1MSTS, OLST, and BBS were 18.1 sec, 20 times, less than 1 sec, and 47, respectively. He could not walk without assistance. After the exercise therapy with the lumbar-type HAL, his locomotive function dramatically improved. TUG, 1MSTS, OLST, and BBS were 12.2 sec, 25 times, 3.9 sec, and 52, respectively. Moreover, the patient could walk 60 meters continuously without assistance. The unique characteristics of the lumbar-type HAL to prevent the lumbar overload and assist the voluntary hip joint motion during exercise therapy may be effective for this patient with lumbar stiffness after LFS. Sit-to-stand training and squat training using the lumbar-type HAL are promising options to improve locomotive function in elderly patients after LFS.