A batch mixer, which includes a floating weight that is freely elevatable by hydraulic cylinders in a hopper which is provided for a mixer main body in a communicated state and into which mixing materials are charged, includes: a linear scale capable of continuously detecting the elevating/lowering position of a floating weight; a position setting device that sets the elevated position of the floating weight; and a control device that controls the elevating/lowering position of the floating weight based on the positional detection signal of the linear scale and the set value of the position setting device. The control device sends a stop signal to a direction switching solenoid valve to stop the action of the hydraulic cylinders when the positional detection signal matches the positional set value. With such a constitution, the stop position of the floating weight can be changed without requiring a complicated work. |