Extendable device

An extendable device, comprising:

• a base member;
• a first ball screw that is provided at a back surface of the base member and that rotates according to a driving force supplied from a drive source;
• a first movable member that is coupled to the base member via the first ball screw and that moves relative to the base member as the first ball screw rotates, the first movable member being a plate-shaped member in parallel to the base member;
• a second ball screw that is provided at a front surface of the first movable member facing the back surface of the base member, and that rotates as the first movable member moves;
• a third ball screw that is provided at the front surface of the first movable member;
• a transmission mechanism that transmits the rotation of the second ball screw to the third ball screw;
• a second movable member that is coupled to the first movable member via the third ball screw and that moves relative to the first movable member as the third ball screw rotates;
• and
• a first guide mechanism that is provided between the base member and the first movable member and that guides the movement of the first movable member with respect to the base member,
• wherein the first ball screw, the second ball screw and the third ball screw are disposed between the first movable member and the base member, and
• the third ball screw and the second movable member are coupled via a through-hole formed in the first movable member.