A catheter (1) for aspiration of foreign matter in a blood vessel is provided with a flexible outer tube (2) and a flexible inner tube (3) inserted into the flexible outer tube (2) and having a front end part capable of protruding beyond the flexible outer tube (2). The outer tube (2) is provided with a guide wire lumen having a front end opening positioned at a peripheral part and near the front end of the outer tube (2) and a rear end opening positioned at a side part which is a base end side at a predetermined distance from the front end opening. The inner tube (3) is provided with a closed front end part (35) and a long side hole (32) having a starting end near the closed front end part (35) and extending to the base end side. The inner tube (3) can slide in the axial direction inside the outer tube (2) and the open area of a side hole that is exposed beyond the front end of the outer tube (2) can be adjusted.
