Device for controlling the trim of a boat including at least one trim tab element or the like, engaged to the transom of the boat by a hinge. At least one actuator is also provided, which is affixed to the transom by an upper terminal and to the tab by a lower terminal respectively through an upper joint and a lower joint. The lower joint includes at least two parts, of which a first part is connected to the lower terminal of the actuator and a second part includes a lower bracket affixed to the tab by fastener means, which are engaged in corresponding engagement seats on the lower bracket and the tab. The first part includes a terminal element, which is provided in a housing seat formed on the lower bracket, such to enable a relative movement of actuator and tab with at least two degrees of freedom.