Provided is an aspiration catheter which does not require a large-scale device, has a largest possible aspiration lumen, and is sufficiently flexible to track tortuous blood vessels following a guidewire, thereby being easily advanced to a target site to be treated.In the aspiration catheter, the tip of the main shaft is obliquely cut, the distal end of the guidewire shaft is positioned at the distal end of the main shaft or protrudes from the distal end of the main shaft in the distal direction, and the relationships 0.5.ltoreq.L2/L1 and L2-L1.ltoreq.5 mm are satisfied, wherein L1 is the length of the obliquely cut portion of the main shaft in the longitudinal direction of the catheter, and L2 is the length from the proximal end of the guidewire shaft to the distal end of the main shaft.