The present invention relates to a synchronous pump structure, particularly to an immersion pump (1) equipped with a float control device (3) and comprising a synchronous electric motor (2) with a permanent magnet rotor (8). The pump (1) is so structured that the float (16) of the control device (3) is incorporated in an envelope (11), externally associated with the body (15) of the pump (1). A sensor element (4) of the control device (3) housed in the pump body (15) in correspondence with the float (16) is also provided.