Provided is a treatment instrument including a guide member with a tip surface to be pressed against an outer surface of a pericardium a pericardium fixing member including at least one needle-shaped portion having a sharp pointed end extending diagonally forward along a circumferential direction at a tip of a cylinder-shaped body rotatable around the axis thereof a perforating member for forming a through-hole for a guide wire in the pericardium to which the pericardium fixing member is fixed and a pointed end position restricting portion for restricting the position of the pointed end in a direction of the axis relative to the tip surface of the guide member at a location where the pointed end of the pericardium fixing member does not reach the outer surface of a heart while the tip surface of the guide member is pressed against the outer surface of the pericardium.
