The present invention relates to an apparatus for sensing and controlling an amount of gas supply and a method for sensing and controlling an amount of gas supply thereby, which can sense a supply amount of the corresponding gas from an optical sensor in real time on the basis of the number of bubbles generated by any set time difference at the time when a target gas flows in a tube in order to differentiate the supply amount more accurately and whether or not the gas supply state is bad, and which can control pressure of the tube in real time by a series of automated devices in order to precisely realize the target supply amount according to gas supply information obtained from the optical sensor, thereby positively preventing malfunction and continuously maintaining the initial set amount of gas supply. The apparatus for sensing and controlling an amount of gas supply includes: a tube (1) for allowing target gas to flow from the bottom to the top; a sensing unit (10) engaged to the external surface of the tube to sense the number of bubbles of the target gas, which sequentially moves for a predetermined period of setting time in the inner space of the tube, in real time by applying an optical sensor based on signal information of a light emitting diode and a transistor, which are positioned to face each other; a controller for receiving the bubble information from the sensing unit to determine whether the bubble information matches the target amount of gas supply in consideration of the predetermined period of setting time; and a pressure controlling unit (20) which is operated by a signal obtained from the controller and varies the number of bubbles during a predetermined period of time by determining the degree of a blocked state of the inner space of the tube through a motor so as to match the varied number of bubbles to the target amount of gas supply.