A diffuser apparatus, comprising: an aeration plate that can be disposed in an aeration tank in order to release pressurized air, fed from a diffusing air feed pipe, as air bubbles from fine pores formed in an aeration plate surface; blow water feeding means for feeding blow water into said diffusing air feed pipe, constituted by a device for feeding blow water to the diffusing air feed pipe via a blow water feed pipe, and formed such that blow water can be fed into the diffusing air feed pipe against an air pressure of the diffusing air feed pipe; and discharging means for discharging said blow water, fed into said diffusing air feed pipe, from said aeration plate, said discharging means being constituted by an inserted pipe, an upper end of which communicates with said aeration plate and a lower end of which is inserted into said diffusing air feed pipe, wherein a lower end surface of said inserted pipe has an inclined suction surface through which said blow water is suctioned and wherein the lower end of the inclined suction surface is positioned 0 mm to 10 mm above the inside bottom of the diffusing air feed pipe, and an upper end of the inserted pipe has an opening facing the aeration plate; wherein the diffusing air feed pipe is provided with a first open/close valve, and the blow water feed pipe is provided with a second open/close valve, wherein during a normal diffusing operation, the first open/close valve is open and the second open/close valve is closed, and wherein during a blowing operation in which water is blown onto the aeration plate, the second open/close valve is opened to feed blow water to the diffusing air feed pipe, whereby diffusing air and blow water are fed to the aeration plate through the inserted pipe. an aeration plate that can be disposed in an aeration tank in order to release pressurized air, fed from a diffusing air feed pipe, as air bubbles from fine pores formed in an aeration plate surface; blow water feeding means for feeding blow water into said diffusing air feed pipe, constituted by a device for feeding blow water to the diffusing air feed pipe via a blow water feed pipe, and formed such that blow water can be fed into the diffusing air feed pipe against an air pressure of the diffusing air feed pipe; and discharging means for discharging said blow water, fed into said diffusing air feed pipe, from said aeration plate, said discharging means being constituted by an inserted pipe, an upper end of which communicates with said aeration plate and a lower end of which is inserted into said diffusing air feed pipe, wherein a lower end surface of said inserted pipe has an inclined suction surface through which said blow water is suctioned and wherein the lower end of the inclined suction surface is positioned 0 mm to 10 mm above the inside bottom of the diffusing air feed pipe, and an upper end of the inserted pipe has an opening facing the aeration plate; wherein the diffusing air feed pipe is provided with a first open/close valve, and the blow water feed pipe is provided with a second open/close valve, wherein during a normal diffusing operation, the first open/close valve is open and the second open/close valve is closed, and wherein during a blowing operation in which water is blown onto the aeration plate, the second open/close valve is opened to feed blow water to the diffusing air feed pipe, whereby diffusing air and blow water are fed to the aeration plate through the inserted pipe.