A compressor includes a casing, a screw rotor, a slide member with at least one economizer port, and a control unit controlling a position of the slide member along the axis of the screw rotor to position the at least one economizer port based on the rotating speed of the screw rotor to advance the timing of opening of the at least one economizer port. The controller controls the position of the slide member along the axis such that the slide member moves upstream toward a suction side of the compressor when the rotating speed of the screw rotor increases, and downstream toward a discharge side of the compressor when the rotating speed of the screw rotor decreases. A refrigerating apparatus includes the compressor, a condenser, a heat exchanger, an expansion unit, and an evaporator, sequentially connected, and has an economizer line.