A bicycle trainer includes a base frame including a first pivot connection part, a damper unit mounted at the base frame, a support frame including a locating portion and a second pivot connection part, which is pivotally connected to the first pivot connection part of the base frame for enabling the support frame to be biased relative to the base frame in direction away from or toward the damper unit such that when the support frame is held in an inclined position relative to the base frame, the locating portion and the damper unit can hold a wheel of a bicycle in place, and a non-return unit mounted at the base frame or support frame and adapted to prohibit the support frame from being biased in direction away from the base frame. The invention enables the support frame to be constrained by the non-return unit.