A functional device for a mobile terminal, the functional device comprising: a housing, comprising a top plate and a bottom plate which are opposite to each other; a functional component, disposed in the housing and movable between a first position at which the functional component is arranged to extend out of the housing and a second position at which the functional component is arranged to retract into the housing; characterized in that, the functional device further comprises: a driving mechanism, disposed in the housing and comprising: a pair of first wheels, connected to the functional component, abutting against an inner wall of the housing and rotatable relative to the housing to drive the functional component to move between the first position and the second position; wherein the pair of first wheels are located at two opposite sides of the functional component; a first shaft, connected between the pair of first wheels, connected to the functional component, and configured to drive the functional component to move; and a driving assembly, connected to at least one of the pair of first wheels and configured to drive at least one of the pair of first wheels to rotate; wherein each of the pair of first wheels is arranged to contact with the housing by a surface contact and abut against both the top plate and the bottom plate, and the functional component is located between the top plate and the bottom plate; or wherein one end of the functional component is provided with the pair of first wheels, each of which is arranged to contact with the housing by a surface contact and abut against one of the top plate and the bottom plate, and the other end of the functional component is slidably connected to the other of the top plate and the bottom plate. a housing, comprising a top plate and a bottom plate which are opposite to each other; a functional component, disposed in the housing and movable between a first position at which the functional component is arranged to extend out of the housing and a second position at which the functional component is arranged to retract into the housing; characterized in that, the functional device further comprises: a driving mechanism, disposed in the housing and comprising: a pair of first wheels, connected to the functional component, abutting against an inner wall of the housing and rotatable relative to the housing to drive the functional component to move between the first position and the second position; wherein the pair of first wheels are located at two opposite sides of the functional component; a first shaft, connected between the pair of first wheels, connected to the functional component, and configured to drive the functional component to move; and a driving assembly, connected to at least one of the pair of first wheels and configured to drive at least one of the pair of first wheels to rotate; a pair of first wheels, connected to the functional component, abutting against an inner wall of the housing and rotatable relative to the housing to drive the functional component to move between the first position and the second position; wherein the pair of first wheels are located at two opposite sides of the functional component; a first shaft, connected between the pair of first wheels, connected to the functional component, and configured to drive the functional component to move; and a driving assembly, connected to at least one of the pair of first wheels and configured to drive at least one of the pair of first wheels to rotate; wherein each of the pair of first wheels is arranged to contact with the housing by a surface contact and abut against both the top plate and the bottom plate, and the functional component is located between the top plate and the bottom plate; or wherein one end of the functional component is provided with the pair of first wheels, each of which is arranged to contact with the housing by a surface contact and abut against one of the top plate and the bottom plate, and the other end of the functional component is slidably connected to the other of the top plate and the bottom plate.