This emitter (120) has a first valve seat part (174) provided around a hole (173) which forms a portion of a flow path between a reduced-pressure flow path and a discharge part. The first valve seat part (174) is formed by a three-step recessed circumferential surface, and is provided with one groove (175) which intersects said three-step recessed circumferential surface, and becomes shallower as said groove approaches the hole (173). As the external liquid pressure increases, a film (140) gradually bends towards the first valve seat part (174), and the open area of the groove (175) gradually decreases. The flow rate of an irrigation liquid is adjusted to an amount capable of passing through the opening of the groove (175).