A brake device of a bait casting reel includes a shoe housing coupled to the spool shaft and having a plurality of pairs of sliding grooves and a plurality of pairs of insertion pins; a plurality of brake shoes slidably received in the sliding grooves and defined with elongate holes in which the insertion pins are inserted; a brake drum defining a plurality of braking surfaces which have different inner diameters; a brake drum moving member into which the brake drum is fitted; a sub cover fixed to a main cover with the brake drum moving member accommodated in the sub cover; springs placed between the brake drum moving member and the sub cover; and a cam member rotatably coupled to the sub cover and defined with a plurality of sets of cam grooves which have different engagement heights.