In a pericardioscopic procedure, without providing an endoscope or surgical instrument with special space ensuring means and without unnecessarily dilating the pericardial space, a space necessary for operation of the endoscope or surgical instrument is ensured, so that maneuverability is improved while suppressing complications. Provided is a space ensuring device comprising: a pericardium pressing part for pressing a pericardium from the pericardial space side a heart pressing part for pressing the surface of a heart from the pericardial space side and an interconnecting part interconnecting the pericardium pressing part and the heart pressing part, wherein the interconnecting part generates the resilient force enabling expansion against a pressure applied by a pericardium and a heart so as to ensure a space between the pericardium pressing part and the heart pressing part.
