PURPOSE: To enable the preventing of bedsore as caused by prolonged lying on a bed effectively without labor by arranging a sheet having a deformable member which is adapted to make an electrode alone conductive at a part on which a load exceeding a bedsore generation pressure works while being exposed to a surface.

CONSTITUTION: When the weight of a patient works on sixteen protrusions 3 unevenly on a cushion 2, the protrusions 3 alone on which a load exceeding a pressure that will develop a bed chafing among those 3 are caused to deform. With the deformation thereof, a moving terminal 4 moves downward vertically within a space 5 and contacts a fixed terminal 6 to be connected to a fixed terminal 6a or 6b so that it is made conductive with a low frequency generator 9 through a lead 7a or 7b and a feeder line 8a or 8b. As the upper end of the moving terminal 4 is exposed on the surface of the protrusion 3, an electrode only at the part on which the load works is made conductive while being exposed on the surface of the cushion 2. When any adjacent protrusion 3 is deformed, a potential difference is generated between the moving terminals 4 and 4 involved and thus, a current flows to a part at which a patient contacting it may cause a bed chafing automatically and selectively from a low frequency generator 9.