A sinusitis treatment device includes: a flexible first elongated body to be guided into an accessory; an imaging unit which is provided on the first elongated long body, for obtaining an image on the front side of a distal end of the first elongated body; a flexible second elongated body having a lumen in which the first elongated body is inserted; an expansive body which is provided on the second elongated body and which has an effective expansive section capable of radial expansive deformation within a natural ostium located between a nasal cavity and an accessory nasal cavity to push open a stenosed part of the natural ostium; and a positioning unit which is provided on the second elongated body, for positioning the effective expansive section of the second elongated long body moved along the first elongated body relative to the first elongated body.