A supporting device (1) for an inner supporting member (2) of an electric household appliance (4), including a support (10) securable, in use, by means of a first part thereof to a fixed guide (5) and by means of a second part thereof, opposite to and facing the first, to a side edge of the inner supporting member, the first and second parts (11,12) being relatively movable in a sliding direction (S) perpendicular to the supporting member, and releasable retaining means (15) for blocking the second part (12) in a plurality of different positions, consisting in a pin (20) carried by the first part (11) overhangingly protruding towards the second in a transversal direction to the fixed guide and sliding against the bias of first elastic means (25) parallelly to the fixed guide; and in a sliding track (22) for a free end of the pin divided into first and second branches (28,29) integrally obtained within the second part (12) of the support (10) and a slide (30) slidingly carried against the bias of second elastic means (33) by such a second part (12) in the sliding direction, respectively; the first branch (28) being provided with a plurality of teeth (35) and first openings (36) facing the second branch (29) and the latter communicating with the first branch through second openings (42) held by the second elastic means (33) in an offset position from the first in the sliding direction.