A blow-off nozzle structure capable of automatically varying the blow-off volume of water comprises a tubular nozzle casing (20) defining a blow-off flow forming passage therein, the passage forming a blow-off opening at a front end thereof and a hot water inlet opening at a rear end thereof, a valve seat (21a) formed in the midst of the blow-off flow forming passage, a valve element (22) capable of being extended to or retracted from said valve seat (21a) so as to adjust the degree of opening of said valve seat, an air mixing portion (10) defined in the blow-off flow forming passage and disposed at a position in front of the valve seat (21a), the air mixing portion (10) communicated with an air intake portion (20b) which has one end opened to atmosphere, and an automatic valve-element reciprocating means (M1) capable of moving said valve element (22) toward or away from said valve seat (21a). Due to such construction, air-mixed water containing a sufficient amount of air can be blown off from the blow-­off opening of the tubular nozzle casing and the volume of the blow-off air-mixed water can be finely and continuously regulated by the control unit corresponding to the degree of opening of said valve seat. The blow-off nozzle structure is especially applicable to a whirlpool bath which gives a remarkable massaging effect to a bather.