A pressure sensor element includes a polymer optical conductor which includes a substrate, a first organic polymer film formed on the substrate, a second organic polymer film superposed on the first organic polymer film, and an optical reflecting film provided on a patterned end face of the first organic polymer film. The first organic polymer film portion within the pattern has a refractive index different from that of the substrate. The first organic polymer film portion outside the pattern has substantially the same refractive index as the substrate. The refractive index of the second organic polymer film is substantially the same as that of the first organic polymer film portion outside the pattern. At least either one of the refractive indexes of the first and second organic polymer films changes with pressure fluctuation.