An optical fiber sensor (8) has an optical fiber (2) and, a light emitting member (3) connected to a first end (20) of the optical fiber (2), a light receiving member (4) connected to a second end (21) of the optical fiber (2). The light emitting member (3) has a light emitting portion (300) through which light is radiated to the first end (20) of the optical fiber (2). The light receiving member (4) has a light receiving portion (400) for receiving light radiated from the second end (21) of the optical fiber (2). The light emitting portion (300) is smaller than a sectional area of a core portion (25) of the optical fiber (2).