A semi-continuous gas-solid fluidized bed separator was newly developed in order to achieve efficient separation of objects with different true specific gravities. A pilot-scale experimental apparatus with variable feeding height of objects was operated. Sand with minimum fluidization velocity of 3.5 cm/s was employed as bed material. Separation of chlorine-free plastics from a mixture of waste plastics containing chlorine-containing plastics was attempted. As a simulated waste plastics mixture, a mixture of Cl-free plastic pellets and Cl-containing plastic pellets was employed. When the plastic mixture was fed at the middle of the bed, the separation time was shortest and separation efficiency was highest. Also, the effect of initial mixture loading on the separation efficiency was evaluated.