An electric household appliance comprising a chamber provided with at least one internal shelf, the internal shelf having a height adjustable resting device comprising a first plate fixable in use against an inner lateral wall of the electric household appliance, in particular a refrigerator or a freezer, and a second plate arranged facing the first plate, on the opposite side of the inner lateral wall of the electric household appliance, and slidingly guided in contact with the first plate along respective longitudinal edges (13,14) of the first plate which are vertically arranged in use; the second plate carrying a resting guide for the shelf on the side opposite to the first plate; wherein: - the first plate is shaped to be arranged in use directly in contact with the inner lateral wall of the electric household appliance, for at least partially covering the same, and has a first face, opposite to said inner lateral wall and facing an opposite second face of the second plate; - the second plate slidingly engagessaid longitudinal edges (13,14) of the first plate; - on said first face, the first plate carries a slider guided so as to slide transversally to said longitudinal edges and integrally provided with a pin, which overhangingly protrudes from the first face; - on its second face, the second plate carries a channel-shaped track describing a closed path on the plane defined by the second face, and slidingly engaged by said pin; - said channel-shaped track comprises first and second branches (26,27) arranged substantially parallel to the longitudinal edges of the first plate and each delimited all along by: an upper edge provided with a plurality of recesses adapted to engage the pin to rest thereon, so that the first plate supports the second plate and the corresponding shelf engaged in the resting guide through the pin and a corresponding recess engaged thereon; and a lower edge provided, at each recess, with at least one pair of abutting surfaces (31,32) for guiding the pin, by virtue of the sliding of the pin, from one recess to the next upon a vertical relative movement between the first and second plates (11,12); characterized in that second plate slidingly engages said longitudinal edges (13,14) of the first plate with respective U-shaped longitudinal edges (19,20) thereof; and in that, in combination, said first and second branches (26,27) of the channel-shaped track are zigzag-shaped along the extension direction of said longitudinal edges (13,14) of the first plate; a third rectilinear branch of said track, open towards a lower edge of the second plate, being arranged by the side of the first branch, adjacent and parallel thereto and directly converging, towards an upper edge of the second plate, into the first branch through an inclined plane obtained on an upper edge of the third branch and directed towards a first of said recesses. - the first plate is shaped to be arranged in use directly in contact with the inner lateral wall of the electric household appliance, for at least partially covering the same, and has a first face, opposite to said inner lateral wall and facing an opposite second face of the second plate; - the second plate slidingly engagessaid longitudinal edges (13,14) of the first plate; - on said first face, the first plate carries a slider guided so as to slide transversally to said longitudinal edges and integrally provided with a pin, which overhangingly protrudes from the first face; - on its second face, the second plate carries a channel-shaped track describing a closed path on the plane defined by the second face, and slidingly engaged by said pin; - said channel-shaped track comprises first and second branches (26,27) arranged substantially parallel to the longitudinal edges of the first plate and each delimited all along by: an upper edge provided with a plurality of recesses adapted to engage the pin to rest thereon, so that the first plate supports the second plate and the corresponding shelf engaged in the resting guide through the pin and a corresponding recess engaged thereon; and a lower edge provided, at each recess, with at least one pair of abutting surfaces (31,32) for guiding the pin, by virtue of the sliding of the pin, from one recess to the next upon a vertical relative movement between the first and second plates (11,12); characterized in that second plate slidingly engages said longitudinal edges (13,14) of the first plate with respective U-shaped longitudinal edges (19,20) thereof; and in that, in combination, said first and second branches (26,27) of the channel-shaped track are zigzag-shaped along the extension direction of said longitudinal edges (13,14) of the first plate; a third rectilinear branch of said track, open towards a lower edge of the second plate, being arranged by the side of the first branch, adjacent and parallel thereto and directly converging, towards an upper edge of the second plate, into the first branch through an inclined plane obtained on an upper edge of the third branch and directed towards a first of said recesses.