The present invention aims to provide an emitter and a drip irrigation tube that can suppress the variations in the discharge amount of the liquid caused by pressure fluctuations of the liquid in the drip irrigation tube. The emitter of the present invention is to be disposed on an inner wall of a tube including a discharge port, for regulating discharge of irrigation liquid from an inside of the tube to an outside of the tube via the discharge port. The emitter includes an intake portion; a regulating unit; a discharge portion; and a flow path. The regulating unit includes a recess; and a film, the film is fixed in a state of covering an inner space of the recess, a region of the film covering the inner space of the recess is a diaphragm portion, the recess has a through hole inside thereof on its bottom surface, the through hole of the recess communicates with the discharge portion, the recess has a slit communicating with the through hole on its bottom surface, and an edge portion forming an upper surface-side opening of the through hole on the bottom surface of the recess, except for the slit, is a valve seat portion for the film. In a state where the emitter is disposed in the tube, when no liquid is present in the tube, the diaphragm portion of the film is not in contact with the valve seat portion, and when the liquid is present in the tube, the diaphragm portion of the film can be in contact with the valve seat portion in accordance with a pressure of the liquid. The diaphragm portion of the film comes into contact with an entire valve seat portion with a time difference.