A venturi nozzle apparatus which is configured to mix water and a gas to dissolve the gas in the water, the venturi nozzle apparatus comprising: a housing in which a flow pipe, through which at least one of the water and the water in which the gas is dissolved selectively flows, and a bypass pipe, which communicates with the flow pipe to selectively bypass at least one of the water and the water in which the gas is dissolved flowing through the flow pipe, are disposed; an injector unit which is detachably inserted into the flow pipe of the housing and configured to selectively receive the gas and the water to dissolve the gas in the water; and a valve member which is inserted into the bypass pipe of the housing and configured to cause at least one of the water and the water in which the gas is dissolved to flow to at least one of the flow pipe of the housing and the bypass pipe of the housing, wherein the flow pipe includes: a supply end portion which is open to allow the water to be selectively supplied; a discharge end portion which is disposed at a position opposite to the supply end portion and which is open to allow the water in which the gas is dissolved to be discharged; and a flow pipe side flow path portion which is provided between the supply end portion and the discharge end portion and through which at least one of the water and the water in which the gas is dissolved selectively flows, wherein the flow pipe side flow path portion includes a step which is formed due to at least a portion of an inner side surface protruding, and wherein, as the injector unit inserted through the supply end portion of the flow pipe is caught at the step, the injector unit is prevented from being detached through the discharge end portion of the flow pipe, characterised in that the venturi nozzle apparatus further comprises a stopper member which is configured to be selectively inserted into the housing to prevent the injector unit inserted through the supply end portion of the flow pipe from being detached through the supply end portion of the flow pipe. a housing in which a flow pipe, through which at least one of the water and the water in which the gas is dissolved selectively flows, and a bypass pipe, which communicates with the flow pipe to selectively bypass at least one of the water and the water in which the gas is dissolved flowing through the flow pipe, are disposed; an injector unit which is detachably inserted into the flow pipe of the housing and configured to selectively receive the gas and the water to dissolve the gas in the water; and a valve member which is inserted into the bypass pipe of the housing and configured to cause at least one of the water and the water in which the gas is dissolved to flow to at least one of the flow pipe of the housing and the bypass pipe of the housing, wherein the flow pipe includes: a supply end portion which is open to allow the water to be selectively supplied; a discharge end portion which is disposed at a position opposite to the supply end portion and which is open to allow the water in which the gas is dissolved to be discharged; and a flow pipe side flow path portion which is provided between the supply end portion and the discharge end portion and through which at least one of the water and the water in which the gas is dissolved selectively flows, a supply end portion which is open to allow the water to be selectively supplied; a discharge end portion which is disposed at a position opposite to the supply end portion and which is open to allow the water in which the gas is dissolved to be discharged; and a flow pipe side flow path portion which is provided between the supply end portion and the discharge end portion and through which at least one of the water and the water in which the gas is dissolved selectively flows, wherein the flow pipe side flow path portion includes a step which is formed due to at least a portion of an inner side surface protruding, and wherein, as the injector unit inserted through the supply end portion of the flow pipe is caught at the step, the injector unit is prevented from being detached through the discharge end portion of the flow pipe, characterised in that the venturi nozzle apparatus further comprises a stopper member which is configured to be selectively inserted into the housing to prevent the injector unit inserted through the supply end portion of the flow pipe from being detached through the supply end portion of the flow pipe.