An input system for a vehicle having a steering wheel, the input system comprising: an input unit comprising a plurality of buttons that are disposable in the steering wheel of the vehicle; and a processor configured to detect an event and to assign a function to at least one of the buttons that corresponds to the detected event, wherein at least one of the plurality of buttons (110L, 110R) comprises: a display portion configured to display an image corresponding to the assigned function, and an operation portion disposed under the display portion, the operation portion including a plurality of protruding members (321 - 328) that are activatable, wherein the plurality of protruding members (321 - 328) are configured, based on the image displayed on the display portion being divided into a plurality of areas, to be activated so as to correspondingly constrain a movement of the display portion relative to the operation portion, the plurality of protruding members being bar-shaped and oriented in at least two directions, and wherein at least one of the protruding members is configured to protrude upward, based upon being activated, to correspondingly constrain the movement of the display portion relative to the operation portion, characterized in that the display portion is configured to pivot, based upon the protruding member being protruded, about a portion of the protruded protruding member. an input unit comprising a plurality of buttons that are disposable in the steering wheel of the vehicle; and a processor configured to detect an event and to assign a function to at least one of the buttons that corresponds to the detected event, wherein at least one of the plurality of buttons (110L, 110R) comprises: a display portion configured to display an image corresponding to the assigned function, and an operation portion disposed under the display portion, the operation portion including a plurality of protruding members (321 - 328) that are activatable, wherein the plurality of protruding members (321 - 328) are configured, based on the image displayed on the display portion being divided into a plurality of areas, to be activated so as to correspondingly constrain a movement of the display portion relative to the operation portion, the plurality of protruding members being bar-shaped and oriented in at least two directions, and a display portion configured to display an image corresponding to the assigned function, and an operation portion disposed under the display portion, the operation portion including a plurality of protruding members (321 - 328) that are activatable, wherein the plurality of protruding members (321 - 328) are configured, based on the image displayed on the display portion being divided into a plurality of areas, to be activated so as to correspondingly constrain a movement of the display portion relative to the operation portion, the plurality of protruding members being bar-shaped and oriented in at least two directions, and wherein at least one of the protruding members is configured to protrude upward, based upon being activated, to correspondingly constrain the movement of the display portion relative to the operation portion, characterized in that the display portion is configured to pivot, based upon the protruding member being protruded, about a portion of the protruded protruding member.