A guide device which can be easily inserted into the interior of the body, can selectively and easily puncture the pericardium even if used by being inserted from the xiphisternum, and can reliably detect that the guide device has reached the interior of the pericardium. A guide device (1) is provided with: a tubular insertion section (2) adapted to be inserted into the interior of the body and open in the vicinity of the tip thereof and on the base end side thereof; a puncture section (3a) provided to the tip of the insertion section (2) and puncturing tissue; a movable section (3) provided to the vicinity of the tip of the insertion section (2) so as to be displaceable between a proximity position at which the movable section (3) is in the proximity of the insertion section (2) and a protruding position at which the movable section (3) protrudes further from the insertion section (2) than the proximity position; a pressing mechanism (4) for pressing the movable section (3) in the direction in which the movable section (3) protrudes from the insertion section (2); and a displacement detection mechanism (5a) for detecting the displacement of the movable section (3) within the interior of the body.
