A nebulizer comprising: a nozzle member for discharging an oxygen gas from an orifice; an aerosol forming member that is disposed at a position corresponding to the orifice of the nozzle member, including a suction pore and a passage continuously formed along the suction pore for sucking water by the oxygen gas flow discharged from the orifice, and a baffle formed at a position separated from the suction pore and opposed to the orifice of the nozzle member so as to allow the sucked water to collide therewith to form fine aerosol; and an air suction pore (9, 10)that sucks air in response to the discharge of the oxygen gas from the orifice of the nozzle member, wherein the nozzle member includes the orifice that discharges the oxygen gas toward the aerosol forming member along an axial core of the nozzle member, characterized in that a flow-out pore of the oxygen gas is formed on a side wall of the nozzle member, in that a valve, disposed on a peripheral portion of the nozzle member at a position opposed to the flow-out pore, closes the flow-out pore in a state where no oxygen gas is supplied to the nozzle member, and opens the flow-out pore in response to a pressure of the oxygen gas supplied to the nozzle member, and in that when the pressure of the oxygen gas supplied to the nozzle element is less than a predetermined value, the oxygen gas is discharged only from the orifice, and when the pressure of the oxygen gas supplied to the nozzle element is higher than the predetermined value, the oxygen gas is discharged from the orifice, while being also allowed to flow out from the flow-out pore to be mixed with the aerosol. a nozzle member for discharging an oxygen gas from an orifice; an aerosol forming member that is disposed at a position corresponding to the orifice of the nozzle member, including a suction pore and a passage continuously formed along the suction pore for sucking water by the oxygen gas flow discharged from the orifice, and a baffle formed at a position separated from the suction pore and opposed to the orifice of the nozzle member so as to allow the sucked water to collide therewith to form fine aerosol; and an air suction pore (9, 10)that sucks air in response to the discharge of the oxygen gas from the orifice of the nozzle member, wherein the nozzle member includes the orifice that discharges the oxygen gas toward the aerosol forming member along an axial core of the nozzle member, characterized in that a flow-out pore of the oxygen gas is formed on a side wall of the nozzle member, in that a valve, disposed on a peripheral portion of the nozzle member at a position opposed to the flow-out pore, closes the flow-out pore in a state where no oxygen gas is supplied to the nozzle member, and opens the flow-out pore in response to a pressure of the oxygen gas supplied to the nozzle member, and in that when the pressure of the oxygen gas supplied to the nozzle element is less than a predetermined value, the oxygen gas is discharged only from the orifice, and when the pressure of the oxygen gas supplied to the nozzle element is higher than the predetermined value, the oxygen gas is discharged from the orifice, while being also allowed to flow out from the flow-out pore to be mixed with the aerosol.