Abstract: A contact pressure detecting sensor having a simplified structure. The sensor includes a pair of air-impermeable sheets and at least one foamed plastic member interposedly arranged between the air-impermeable sheets while being kept from being uncompressed. The foamed plastic member is capable of resuming its original configuration after compression. The sensor also includes at least one tube arranged so as to extend from the vicinity of the foamed plastic member to outside the air-impermeable sheets. The air-impermeable sheets are joined to each other at portions thereof positioned around the foamed plastic member and tube.