An elongated probe to be inserted into a tube which is open at a distal end portion of an insertion section of an endoscope includes a sheath constituting the outer circumferential surface of the optical probe, an optical fiber laid in the internal space of the sheath along the longitudinal direction of the sheath, and a deflection scanning means disposed in the internal space of the sheath to deflect light outputted from the optical fiber and is rotated around an axis line extending in the longitudinal direction to scan the deflected light in a circumferential direction of the axis line. A plurality of light transmission sections for transmitting the scanning light is provided, each formed flat on the outer surface, on a side wall of the sheath along the circumferential direction.