To provide a retraction preventing mechanism by which a wheelchair can stop not to be retreated on the spot even without releasing hands from wheels or performing a braking operation at the time of traveling on a slope such as an uphill road.

In this retraction preventing mechanism which is attached near wheelchair wheels symmetrically and prevents the retreat rotation of the wheels capable of operating advance rotation on the slope such as the uphill road, a spindle 2, a stopper attaching shaft 3 and a magnet 4 for stopper attraction are fixed to an attaching member 1 provided with egg-shaped attaching holes 1a roughly with a gap, a stopper 5 formed by integrating a blocking part 5a and a framed magnet part 5b in a hinge shape is attached to the stopper attaching shaft 3 turnably between the spindle 2 and the magnet 4 for the stopper attraction and the structure of the retraction preventing mechanism main body P of the wheelchair is attained.