The invention discloses an arm support sensing device, which comprises a sensing switch and a floating mechanism with the sensing switch being installed along the down-press direction of an arm support in a floating way, wherein the floating mechanism comprises an installation seat, a floating part and an elastic element, wherein the installation seat is fixedly connected onto a arm support bracket; the floating part is movably connected to the installation seat, and the sensing switch is connected with the floating part in a synchronous movement way; and the elastic element is arranged between the installation seat and the floating part, and the sensing switch has a movement trend towards the arm support. Through the floating mechanism, the accidental damage of the sensing switch caused by the floatation of the arm support can be completely avoided.