In the present invention, disclosed is an endovascular treatment aid with which it can be confirmed that the endovascular treatment aid is in close contact with a blood vessel, and leakage of a captured substance is prevented. The endovascular treatment aid is provided with: a flexible shaft； a filter that is fixed to the shaft so as to form an opening on a proximal end side, that when opened assumes a conical shape the bottom surface of which is a ring which has elastic restoring force and which is fixed to the opening, and that can be opened or closed in the shape of an umbrella； and linear support members that are each fixed so as to connect the ring and a part of the shaft, and that make it possible to close the filter with the application of an external force to the proximal end side. A coil composed of a radiopaque material is wound about the ring. When the filter is closed, the ring assumes a shape in which a plurality of mountains oriented toward the distal end side and a plurality of valleys oriented toward the proximal end side are alternately generated, and the mountains and valleys are made to be close to one another. The coil is disposed on the ring so as to include a position fixed by the support members which are on the ring, and so as not to include the positions of the vertices of the mountains and the vertices of the valleys.
