A sheet pressure sensor includes a first fiber layer, a second fiber layer, and a third fiber layer provided between the first and second fiber layers. The third fiber layer has connecting yarns that electrically connect first conductive portions of the first fiber layer and the second conductive portion in the second fiber layer with a predetermined electric resistivity. The sheet pressure sensor further includes a measuring instrument for measuring electric resistance between at least one of the first conductive portions and the second conductive portion. The connecting yarns unstrain due to deformation of the first or second conductive portion which is generated by applied pressure, and then are short-circuited with one of them. The sheet pressure sensor can detect the pressure while keeping air ventilation characteristic by giving a pressure detection function to the fiber layers.
