A magnetic tape cartridge comprises: a reel 2 around which a magnetic tape MT is wound; a cartridge case 1 for accommodating the reel 2 in a locked state; and a release pad 5 inserted into a cup-shaped hub 2A of the reel 2 in a locked state of the reel 2. The release pad 5 includes a pad body 5A having a plurality of corners to be faced proximately to the inner peripheral surface 2C of the cup-shaped hub 2A, and a plurality of lock releasing pins 5B projecting downwardly from a bottom surface of the pad body 5A at the respective corners and inserted through a bottom surface of the cup-shaped hub 2A. The release pad 5 is provided with a flank 5E extending from each corner downwardly through the respective lock release pin 5B so that an assembling clearance is formed with respect to an inner periphery of a flange 2G position in an open side of the cup-shaped hub 2A.