Fastening device for people with reduced mobility conditions, of the variety employed in chairs or arm chairs in domestic, geriatric, care or hospital environments, comprising fixation means (50), which can be adapted to the back of the chair or arm chair and containing means (100) to contain the person to be fastened. Said device (1) comprises a portable support body (10) in which said fixation means (50) and containing means (100) are located and the containing means (100) comprise at least one containing strap (101, 102, 103) connected to an emergency locking retractor (104, 105, 106) which is configured in order to facilitate the free movement of the person fastened to said chair or arm chair and to prevent falling movement of the same.
