Abstract: A constant liquid feeding device of the invention comprises a flow meter for measuring quantity of liquid flowing through a pipe, a valve attached to the pipe, a valve control device attached to the valve for opening and closing the pipe, an operating device having a feeding switch and a learning switch, and a control unit electrically connected to the operating device and the valve control device. The control unit is provided with a first memory, a second memory and a comparing device for comparing data stored in the first and second memories. When the learning switch is actuated, the control unit operates to memorize an amount of liquid flowing through the flow meter in the first memory, wherein the amount of liquid is manually controlled by the valve control device. When the learning switch is not actuated, the control unit checks if the feeding switch is turned on.