Abstract: A slide projector which is adapted for the use of circular trays (10, 12) having different numbers of slide compartments and which includes a pulse-controlled electronic switch unit for controlling a transport motor selectively moving one of the trays (10, 12) forwardly or backwardly comprises a slider (30) for fixing the trays (10, 12) in position, which slider can be actuated by the electronic switch unit following each indexing of the tray and which can be brought into engagement with both transport pins (15) associated with the compartments of the first circular tray (10) and serving as transport and fixing means and with a toothing (17) associated with the compartments of the second circular tray (12) and serving as transport and fixing means, following each indexing of the tray such engagement being achieved by fixing means (34, 35) associated with the transport and fixing means (15, 17) of the trays and adapted to the shape and size thereof.