A magnetic tape cartridge includes a substantially rectangular box shaped case that houses, inside a housing area, a single reel wound with a magnetic tape and equipped with a reel plate that is attracted and held by magnetic force when loaded into a drive device, and a metal-containing block that is disposed inside the case and outside the housing area of the reel, and has a proportion of metal by mass to a total mass of metal provided inside the case including the reel equipped with the magnetic tape and the reel plate of 18% or greater.

A magnetic tape cartridge includes a substantially rectangular box shaped case that houses, inside a housing area, a single reel wound with a magnetic tape and equipped with a reel plate that is attracted and held by magnetic force when loaded into a drive device, and a metal-containing block that is disposed inside the case and outside the housing area of the reel, and has a proportion of metal by mass to a total mass of metal provided inside the case including the reel equipped with the magnetic tape and the reel plate of 18% or greater.