Provided is a catheter that includes a catheter tube and a temperature sensor. The catheter tube includes a tip-flexible part and a base end part. The base end part includes a first base end section having rigidity higher than the tip-flexible part, and a second base end section having rigidity lower than the first base end section. The tip-flexible part has an axial length from 40 mm to 100 mm, the first base end section has an axial length from 200 mm to 400 mm, and the second base end section has an axial length from 200 mm to 900 mm. A value of the rigidity of each of the first and the second base end sections decreases linearly from the first base end section to the second base end section, in a region around a boundary between the first base end section and the second base end section.
