<p>Disclosed are a surface plasmon humidity sensor with which sensitivity to humidity can be improved, a surface plasmon humidity sensor, an optical fiber type of humidity sensor, and a humidity measurement device. A sensor part SP arranged midway on optical fibers (20a, 20b) has a hetero-core part (3) that causes part of the transmitted light to interact with the outside. A metal film (50) that generates surface plasmons by reflecting the light in a light transmissive member on the outer peripheral surface of said hetero-core part (3) is formed on said outer peripheral surface. A film (60) whose refractive index changes according to the humidity in the atmosphere is formed on the outer peripheral surface of metal film (50).</p>
