For the purpose of facilitating the introduction of a thin wire into a thin vessel, guided by a guide wireThe vascular optical device according to the present invention isThe longitudinal lumen (4) andA long sheath (6) having an arcuate groove (5) disposed along the longitudinal direction in parallel to the lumen (4) andHoused in lumen (4)；An illumination part (8) for directing illumination light to an object in the blood vessel from the outside or an optical member (7) comprising at least one of a light detecting part (9) which directs the return light from the subject to the outside in the outside is provided.Ali grooveThe transverse cross section of the long member (3) has a transverse cross-sectional shape that can be accommodated in the longitudinal direction.On the other side of rumenAn opening (10) having a width dimension smaller than the diameter of a long member (3) to protrude an outer portion in the circumferential direction of the long member (3) accommodated therein is provided.Sheath (6)From the direction of arrangement of lumen (4) and ant grooveIt has small outer dimensions in the direction perpendicular to the array direction.ガイドワイヤによって案内しながらより細い血管内への導入を容易にすることを目的として、本発明に係る血管用光学装置（２）は、長手方向に貫通するルーメン（４）と、ルーメン（４）に並列して長手方向に沿って設けられたアリ溝（５）とを備える長尺のシース（６）と、ルーメン（４）内に収容され、体外から血管内の被写体に照明光を導く照明部（８）または被写体からの戻り光を体外に導く光検出部（９）の少なくとも一方からなる光学部材（７）とを備え、アリ溝（５）が、横断面円形の長尺部材（３）を長手方向に移動可能に収容可能な横断面形状を有するとともに、ルーメン（４）とは反対側に、収容した長尺部材（３）の周方向の一部を外部に突出させる長尺部材（３）の直径より小さい幅寸法の開口部（１０）を有し、シース（６）が、ルーメン（４）とアリ溝（５）との配列方向より、配列方向に直交する方向に小さい外形寸法を有する。
