The present invention provides lock release means that allows spring constant of the lock release means to be set to any desired value without regard to a material used for a cartridge holder. A disk recording and/or reproducing apparatus includes: recording and/or reproducing means disposed in a chassis; a cartridge holder supported on the chassis movably between an insertion and withdrawal position, at which a disk cartridge is inserted or removed, and a recording and reproducing position, at which the disk cartridge is recorded or reproduced by the recording and/or reproducing means; an eject lever disposed on an upper surface of the chassis so as to be movable in a disk cartridge insertion and withdrawal direction; eject lever lock means disposed on the upper surface of the chassis; and lock release means mounted on the cartridge holder such that a leading end side of the lock release means advances into the cartridge holder from an upper surface of the cartridge holder.