An otorhinolaryngological treatment device includes: a flexible elongated body to be introduced into an accessory nasal cavity through a nasal cavity; an expansion body which is provided on the elongated body and has an effective expansive section capable of radial expansive deformation within a natural ostium between the nasal cavity and the accessory nasal cavity to thereby force open a stenosed part of the natural ostium; and imaging unit for obtaining an image on the front side of a distal end of the elongated body, which is provided integrally with the elongated body on the distal side of the elongated body relative to the expansion body. The treatment device enables easy positioning (aligning) of the expansion body inside the nasal cavity, without need for radioscopy.