To provide an apparatus for fixing an onboard wheelchair which can simply and surely fix and separate the wheelchair which gets in a vehicle or gets on or off the vehicle, to the floor of the vehicle and can deal with the fixation of even the wheelchair of a different size.

The apparatus for fixing the on-vehicle wheelchair comprises a mounting unit 1 mounted in a frame 4 of the wheelchair (b) which gets in the vehicle, a body 2 provided at a substantially intermediate part of both wheels 6 and 7 of the wheelchair on the floor of the vehicle, and a tensioning means 3 mounted at the body to engage its locking member 14 with the mounting unit 1. The mounting unit is provided substantially parallel to an axle 7a of rear wheels between front wheels and rear wheels of the wheelchair. The locking member of the tensioning means is arranged so as to operate a towing force of the tensioning means at the mounting unit substantially just under the mounting unit via a detouring member 17 provided at the body.