Abstract: Provided is a detector, a gas scrubber comprising the detector for identifying a residual lifetime of an absorbent material contained in a gas scrubber for purifying a harmful exhaust gas, and a method of identifying the residual lifetime of the absorbent material. The detector comprises a solid chemical material, the color of which changes when it comes in contact with the untreated exhaust gas due to loss of absorbing power of the absorbent material, a detection window containing the solid chemical material therein, therethrough the visual identification of the color change of the solid chemical material can be made, and connecting units placed on an upper and lower end of the detection window. The visual identification of the color change of the solid chemical material through the detection window enables the continuous and safe identification of the residual lifetime of the absorbent material and the replacement time, thereby increasing the reliability of the gas scrubber.