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 the temperature of the liquid in the drip irrigation tube. The emitter (120) of the present invention is disposed on an inner wall of a tube (110) including a discharge port (112), for regulating discharge of irrigation liquid from an inside of the tube (110) to an outside of the tube (110) via the discharge port (112). The emitter (120) 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, and a region of the film covering the inner space of the recess is a diaphragm portion. The flow path has a decompression region for decompressing the taken-in liquid, the decompression region has a serpentine shape, and in the decompression region, a fluctuation ratio of a cross-sectional area in a direction perpendicular to an axial direction is within a range of 1±0.1 with reference to a smallest cross-sectional area.
