A catheter includes: a tubular insertion section configured to be inserted into a body； an expandable and contractible balloon that is disposed at a distal end portion of the insertion section to communicate with lumen of the insertion section； a knife wire that is disposed at the distal end portion of the insertion section and configured to treat a biological tissue； and an operation section that is disposed at a proximal end portion of the insertion section and configured to operate the balloon and the knife wire. The operation section includes a connecting portion that is fitted to a fluid discharge port of a pressurizer capable of supplying a fluid for causing the balloon to expand and a fixing tool which is configured to fix the operation section to the pressurizer to be detachable therefrom.
