Disclosed is an apparatus for preventing backlash of a spool used in a baitcasting reel. A movable cam 20 assembled to a stationary cam 10 secured to a spool shaft movesin a direction parallel with the spool shaft, when a revolution of the spool is increased. A braking plate 30 approaches a permanent magnet 2a of a spool cover, so that the spool is smoothly and precisely braked.