An extendable mechanism may include an extension member. The extendable mechanism may further include a link member which is provided with an extension-member-guide element. The extension member may be in engagement with the extension-member-guide element of the link member in a manner so as to be retractably extendable from the link member in an extension direction along an axis of the extension member. The extendable mechanism may further include a link-member-guide element for being disposed at the body structure. The link member may be in engagement with the link-member-guide element in a manner so as to be retractably extendable from the link-member-guide element in the extension direction. The extendable mechanism may further include a biasing member for being arranged between the link member and the body structure. A controller may include a controller body and the extendable mechanism.