Abstract: The knife comprises a substantially hollow handle, a knife blade guided longitudinally movable in a knife blade guide track and at least one guided slider member coupled indirectly with the handle end of the longitudinally movable knife blade. A slider longitudinal slot which receives the slider member extends across the entire thickness of the handle. The slider member has an operating piece on each handle broad side. Both operating pieces receive between themselves at least one guide strip extending parallel to the handle longitudinal axis. The knife blade is held between both operating pieces. The knife blade is so structured that an ergonomically beneficial thumb operable slider mechanism operation is provided for a variety of working situations in a simple way.