A catheter comprising: a tube having a lumen in an interior thereof and a peripheral wall portion surrounding the lumen; a guide wire port formed in a midway position in an axial line direction of the tube, the guide wire port penetrating the peripheral wall portion; and a core wire inserted into the lumen and extending across the guide wire port in the axial line direction; and characterized in that , the core wire includes a leading end side area , which is an area positioned further to a leading end side than the guide wire port, and a tapered area , which is an area further to a base end side than the leading end side area and which is formed such that a cross-sectional area thereof in a direction orthogonal to the axial line direction becomes continuously larger from the leading end side toward the base end side, the tapered area includes a first tapered area , which is an area extending from a base end of the leading end side area toward the base end side, and which is an area including a same position as the guide wire port in the axial line direction, and a second tapered area , which is an area extending from a base end of the first tapered area toward the base end side, and a rate of increase of the cross-sectional area from the leading end side toward the base end side in the first tapered area is larger than a rate of increase of the cross-sectional area from the leading end side toward the base end side in the second tapered area. a tube having a lumen in an interior thereof and a peripheral wall portion surrounding the lumen; a guide wire port formed in a midway position in an axial line direction of the tube, the guide wire port penetrating the peripheral wall portion; and a core wire inserted into the lumen and extending across the guide wire port in the axial line direction; and characterized in that , the core wire includes a leading end side area , which is an area positioned further to a leading end side than the guide wire port, and a tapered area , which is an area further to a base end side than the leading end side area and which is formed such that a cross-sectional area thereof in a direction orthogonal to the axial line direction becomes continuously larger from the leading end side toward the base end side, a leading end side area , which is an area positioned further to a leading end side than the guide wire port, and a tapered area , which is an area further to a base end side than the leading end side area and which is formed such that a cross-sectional area thereof in a direction orthogonal to the axial line direction becomes continuously larger from the leading end side toward the base end side, the tapered area includes a first tapered area , which is an area extending from a base end of the leading end side area toward the base end side, and which is an area including a same position as the guide wire port in the axial line direction, and a second tapered area , which is an area extending from a base end of the first tapered area toward the base end side, and a first tapered area , which is an area extending from a base end of the leading end side area toward the base end side, and which is an area including a same position as the guide wire port in the axial line direction, and a second tapered area , which is an area extending from a base end of the first tapered area toward the base end side, and a rate of increase of the cross-sectional area from the leading end side toward the base end side in the first tapered area is larger than a rate of increase of the cross-sectional area from the leading end side toward the base end side in the second tapered area. <EOS>