A catheter that is guided into an intra-corporeal passageway is set forth. A catheter tube accommodates an element having a piston for detecting a pressure in the intra-corporeal passageway. Silicone gel is accommodated in the catheter tube to transmit the detected pressure in the catheter tube. A strain gage is disposed on a semiconductor chip to output an electric signal based on an amount of a deformation thereof indicative of the pressure in the catheter tube.
