A diagnosis catheter 1 for an interstitial cystitis is connected to a current perception threshold inspection apparatus 4. A catheter body 11 is made of a soft flexible material and includes a bladder-dwelling distal end section A and a diagnosis section B adjacent the distal end section A at a proximal end side of the body 11. A core member 12 is made of a hard flexible material and is inserted into the diagnosis section B in the catheter body 11. An inflatable balloon 13 is mounted on an outer periphery around the bladder-dwelling distal end section A of the catheter body 11. A fluid supply passage 16 is provided in the catheter body 11 so that an end of the passage 16 is communicated to the balloon 13 and a proximal end of the passage 16 is communicated to an injection part 17.