Fiber unit

A fiber unit having one or a plurality of illumination fibers and a plurality of detection fibers and provided in a measurement probe that performs optical measurement by inputting and outputting light from a distal end thereof, wherein each of the illumination fibers and the detection fibers comprises:

• a soft portion that is bendable;
• a distal end hard portion provided at an end thereof and having a greater hardness than the soft portion;
• and
• a pitch conversion portion that connects the soft portion and the distal end hard portion and changes a distance between adjacent fibers at the distal end hard portion with respect to a distance between the adjacent fibers at the soft portion, by bending and extending,
• wherein when a most inclined angle of angles each formed by a central axis of the distal end hard portion and a line segment connecting an end portion of the pitch conversion portion closer to the soft portion and an end portion of the pitch conversion portion closer the distal end hard portion is denoted by Deg_max, the following is satisfied:
• 1.0 degree<Deg_max<6.0 degrees.