Abstract: An arm mechanism includes a first arm, which is hollow, a second arm, and a connection portion for mutually rotatably connecting the first arm and the second arm. A connection portion 15 includes a rotary shaft extending in a direction perpendicular to an axial direction of a first arm 11 and a second arm 12, a friction portion for generating a frictional force against rotation of the rotary shaft, and a biasing member which is housed in the first arm, has an end portion facing away from the rotary shaft and connected to the first arm, has an end portion facing the rotary shaft and connected to the second arm via a connection member, and generates a contraction force which is increased with an increase in angle between an axis of the second arm and an axis of the first arm by rotation of the rotary shaft.