WE CLAIM:
1. A filter device, comprising:
a core member;
a push member fixed to said core member;
a first tube disposed proximally of said push member in the longitudinal direction and movable along said core member;
a second tube disposed distally of said push member in the longitudinal s.
direction and movable along said core member;
a third tube movable along said first tube;
a first restriction member disposed on said first tube and configured to restrict a pushing movement of said third tube to the distal direction of said first restriction member;
a filter having a closed end distally of said push member in the longitudinal direction and disposed to have an opening at the proximal end of said filter;
a ring fixed to said opening and having elasticity or shape-memory ability;
two first wires, one end of each first wire being fixed to said third tube, and the other end being fixed to part of said ring; and
two second wires, one end of each second wire being fixed to part of said ring, and the other end being fixed to said second tube;
wherein said filter is configured in such a manner that the diameter of said opening is reduced by deformation of the shape of said ring, the deformation being caused by said first wires and said second wires when said push member fixed to said core member is pushed with said push member in contact with said second tube, and in such a manner that the diameter of said opening is expanded by restoration of said ring to the original shape, the restoration being caused by separating said push member fixed to said core member from said second tube.

2. The filter device according to claim 1, wherein the positions at which said first wires are fixed to the said ring and the positions at which said second wires are fixed to said ring are arranged alternately in relation to the central axis of said core member.
3. The filter device according to claim 1 or 2, wherein a second restriction member is fixed to said first tube and configured to restrict the movement of said third tube to a proximal portion of said first tube in the longitudinal direction.
4. The filter device according to any one of claims 1 to 3, wherein a spring-like member is fixed to a proximal portion of said core member in the longitudinal direction.
5. The filter device according to any one of claims 1 to 4, wherein a flexible member is fixed to a distal portion of said core member in the longitudinal direction.
6. The filter device according to any one of claims 1 to 4, comprising: a double lumen tube having a first lumen into which a guidewire can be inserted and a second lumen into which said core member can be inserted,
wherein said double lumen tube is fixed to a distal portion of said second tube in the longitudinal direction: