Device (2; 102; 202; 302; 402; 502; 602; 702; 802; 902) for maintaining a door of a motor vehicle in an ajar position with respect to a body element during the manufacture of this motor vehicle, including: - a body; - fastening means (10; 110; 210; 310; 410; 510; 610; 710) designed to fasten the body on the door on a fastening area disposed inside the vehicle; comprising at least a first locking member (22; 122; 222; 322; 422; 522; 622) mounted on the body 8, the first locking member (22; 122; 222; 322; 422; 522; 622) having a locking portion (22a; 122a; 222a; 322a; 422a; 522a; 622a) and being movable between: - an unlocked position in which the locking portion (22a; 122a; 222a; 322a; 422a; 522a; 622a) is likely to pass through an opening formed in the door; and - a locked position in which the locking portion (22a; 122a; 222a; 322a; 422a; 522a; 622a) is likely to bear against the door in order to ensure the fastening of the body to the door; the first locking member (22; 122; 402; 522) having an actuating portion (22b; 122b; 402b; 522b) designed to be actuated by a user so as to move the first locking member (22; 122; 402; 522) between the unlocked position and the locked position, or vice versa; - a holding member (26; 826) mounted on the body and arranged to bear on a first side of the body element and hold the door in the ajar position; and - an abutment member mounted on the body and arranged to extend at a distance from the door so as to delimit a space between the abutment member and the door, the abutment member being arranged to bear on a second side of the body element and prevent the closing of the door; characterized in that the first locking member is pivotally mounted about an axis (22c; 122c) arranged to extend parallel to the opening formed in the door; and in that the locking portion (22a; 122a) and the actuating portion (22b; 122b) of the first locking member (22; 122) extend on both sides of the axis (22c; 122c). - a body; - fastening means (10; 110; 210; 310; 410; 510; 610; 710) designed to fasten the body on the door on a fastening area disposed inside the vehicle; comprising at least a first locking member (22; 122; 222; 322; 422; 522; 622) mounted on the body 8, the first locking member (22; 122; 222; 322; 422; 522; 622) having a locking portion (22a; 122a; 222a; 322a; 422a; 522a; 622a) and being movable between: - an unlocked position in which the locking portion (22a; 122a; 222a; 322a; 422a; 522a; 622a) is likely to pass through an opening formed in the door; and - a locked position in which the locking portion (22a; 122a; 222a; 322a; 422a; 522a; 622a) is likely to bear against the door in order to ensure the fastening of the body to the door; the first locking member (22; 122; 402; 522) having an actuating portion (22b; 122b; 402b; 522b) designed to be actuated by a user so as to move the first locking member (22; 122; 402; 522) between the unlocked position and the locked position, or vice versa; - an unlocked position in which the locking portion (22a; 122a; 222a; 322a; 422a; 522a; 622a) is likely to pass through an opening formed in the door; and - a locked position in which the locking portion (22a; 122a; 222a; 322a; 422a; 522a; 622a) is likely to bear against the door in order to ensure the fastening of the body to the door; - a holding member (26; 826) mounted on the body and arranged to bear on a first side of the body element and hold the door in the ajar position; and - an abutment member mounted on the body and arranged to extend at a distance from the door so as to delimit a space between the abutment member and the door, the abutment member being arranged to bear on a second side of the body element and prevent the closing of the door;