A handheld electronic device suitable for being installed on a holder, wherein the holder comprises a second locking part having an assembling opening and an assembling space behind the assembling opening, an area of a projection of the assembling space on a plane (s) where the assembling opening is located is greater and lies over the area of the assembling opening, the handheld electronic device comprising: a first locking part disposed at a back side of the handheld electronic device, wherein the first locking part comprises a head portion and a necking portion connected between the handheld electronic device and the head portion, and wherein the head portion of the first locking part is adapted to enter the assembling space of the second locking part through the assembling opening along an assembling direction and then reach a locking position in the assembling space by moving along an engaging direction parallel to the plane where the assembling opening is located; characterized in that said handheld electronic device further comprises a first decoration plate having an outer surface opposite to a main body of said handheld electronic device and an electrode contact on the outer surface, which is electrically connected to the handheld electronic device; a decoration ring disposed at the back side of the handheld electronic device and surrounding the first locking part to form an accommodating space; and a first elastic component disposed between said main body of the handheld electronic device and the first decoration plate so as to provide a returning force to the first decoration plate in operation; wherein the first decoration plate is disposed at an opening of said accommodating space and has a through hole exposing the head portion of the first locking part, the first locking part is located in the accommodating space, and the second locking part is configured to enter the accommodating space after the head portion of the first locking part enters the assembling space through the assembling opening along the assembling direction. a first locking part disposed at a back side of the handheld electronic device, wherein the first locking part comprises a head portion and a necking portion connected between the handheld electronic device and the head portion, and wherein the head portion of the first locking part is adapted to enter the assembling space of the second locking part through the assembling opening along an assembling direction and then reach a locking position in the assembling space by moving along an engaging direction parallel to the plane where the assembling opening is located; characterized in that said handheld electronic device further comprises a first decoration plate having an outer surface opposite to a main body of said handheld electronic device and an electrode contact on the outer surface, which is electrically connected to the handheld electronic device; a decoration ring disposed at the back side of the handheld electronic device and surrounding the first locking part to form an accommodating space; and a first elastic component disposed between said main body of the handheld electronic device and the first decoration plate so as to provide a returning force to the first decoration plate in operation; wherein the first decoration plate is disposed at an opening of said accommodating space and has a through hole exposing the head portion of the first locking part, the first locking part is located in the accommodating space, and the second locking part is configured to enter the accommodating space after the head portion of the first locking part enters the assembling space through the assembling opening along the assembling direction.