Active bending section, insertion part and endoscope

The invention provides an active bending section, an insertion part and an endoscope, and relates to the technical field of endoscopes, the active bending section comprises a plurality of snake joints and a limiting piece, the snake joints are connected in sequence, the adjacent snake joints are in running fit through hinge parts, and a running gap is formed between the adjacent snake joints; the limiting piece is installed on the snake joints, the limiting piece has a first state and a second state, the limiting piece can be switched between the first state and the second state, and under the condition that the limiting piece is in the first state, the limiting piece is matched with the other adjacent snake joint in a limiting mode so as to limit relative rotation of the two adjacent snake joints through the hinge parts; under the condition that the limiting piece is in the second state, the limiting fit between the two adjacent snake bone sections is relieved, so that the adjacent snake bone sections can co