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.