A retaining unit (1) for retaining a container (4), comprising a supporting body (7), mountable on a movement unit (5), a gripping element (8) and a resting element (9) mounted on the supporting body (7), The gripping element (8) comprises a first arm (10) and a second arm (11), comprising respective gripping portions delimiting a housing (14) for the container (4), having a vertical main line of extension (15). The first arm (10) is movable between a first returned position and a first opened wide position. The resting element (9) has a resting portion (35), delimiting the housing (14), in part, and configured to make contact with a lateral surface of the container (4), is rotatably mounted on the supporting body (7) according to an axis of oscillation (36) transversal to the main line of extension (15), and can oscillate around this between multiple operating positions at each of which the resting portion (35) is positioned differently and delimits the housing (14) differently.