Disclosed is a fiber unit (310), which is provided in a measuring probe (3) that performs optical measurement by having light inputted and outputted from the leading end of the measuring probe, and which has a lighting fiber (311) and a plurality of light receiving fibers. Each of the lighting fiber (311) and a plurality of detecting fibers is provided with: a bendable soft portion (331) a leading end hard portion (332) having hardness higher than that of the soft portion (331) and a pitch conversion portion (333), which connects the soft portion (331) and the leading end hard portion (332) to each other, and which changes the distances among other adjacent fibers in the leading end hard portion (332) with respect to the distances among the adjacent fibers in the soft portion (331) by extending in a bent state. When Deg_max represents a most steep angle among the angles formed between the center axis of the leading end hard portion (332) and a line segment formed by connecting, in the pitch conversion portion (333), an end portion on the soft portion (331) side, and an end portion on the leading end hard portion (332) side, formula 1.0
