Abstract: A valve actuator device includes a supporting body, a driving shaft, and a fluid cylinder having a body connected to one side of the supporting body. The cylinder has a rod that controls rotation of a driving arm rigidly connected to the driving shaft. Linear movement of the rod is converted into rotation of the driving arm by engagement of a cam-follower pin carried by the rod within a slot formed in the driving arm. The slot is formed in an insert that constitutes an element separate from the driving arm body and that is received and held within a seat of the driving arm body. Thus, a single main body for the driving arm is provided, having a plurality of inserts for selective mounting within the seat and are differentiated from one another in the dimensions and shape of the slot and/or in the material of the insert.