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 in the drip irrigation tube. The emitter (120) of the present invention is an emitter for regulating discharge of irrigation liquid. The emitter (120) includes an intake portion for taking in the liquid in the tube (110)； a regulating unit that regulates a discharge amount of the liquid； a discharge portion for discharging the liquid via a discharge port (112) of the tube (110)； and a flow path communicating the intake portion and the regulating unit. 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 communicating with the discharge portion and a plurality of slits communicating with the through hole, and an edge portion forming an upper surface-side opening of the through hole, excluding the plurality of slits, is a valve seat portion. When the diaphragm portion of the film comes into contact with the valve seat portion, the film and the slits form communication ports to the through hole, and each slit serves as a flow path to the through hole. The emitter (120) satisfies condition (1):Condition (1): Assuming a cross-sectional area of the communication port formed by the film and the slit required when the emitter has one slit to be 1, a cross-sectional area of a communication port to the through hole formed by the film and each slit is less than 1.
