An endoscope and a surgical instrument are easily manipulated to desired positions and orientations independently while the state of treatment with the surgical instrument can be easily observed using an endoscopic image. Provided is a medical-device guiding method comprising a U-shape forming step of placing both ends of a guide wire outside the pericardium and placing the guide wire, with an intermediate portion curved in a substantially U-shape in the pericardial cavity an endoscope inserting step of inserting an endoscope into the pericardial cavity along the guide wire from one end of the ends placed outside the pericardium in the U-shape forming step a guide-unit inserting step of inserting the guide unit into the pericardial cavity along the guide wire from the other of the ends placed outside the pericardium in the U-shape forming step and an opposing step of opposing the distal end portions of the endoscope and the guide unit, which are inserted into the pericardial cavity in the endoscope inserting step and the guide-unit inserting step, respectively, at intermediate positions of the guide wire.
