In a signal recording or reproduction device for disks, release means for disengaging a lock slide from a holder when the holder is pivotally moved upward from a lowered position has a release piece slanting with respect to a plane containing a path of pivotal movement of the holder, attached at a base end thereof to a chassis and deformable by deflecting outward. The release piece extends from its base end along cartridge inserting and unloading directions. The release piece escapes from the lock slide by being deflected outward for deformation by contact with the lock slide when the slide is moved with the descent of the holder, and restores itself elastically upon passage of the lock slide. The lock slide as brought into contact with the lower end of the release piece when the holder is pivotally raised from the lowered position is disengaged from the holder by being so deflected for deformation.