Insert, optical insert, and photoacoustic measurement device

An insert of which at least a portion is inserted into a subject, the insert comprising:

• a hollow needle tube that has an inclined surface comprising a leading end opening at a leading end;
• a long needle base that has a chamber whose leading end communicates with an inside of the needle tube and holds a rear end portion of the needle tube;
• and
• a light introduction portion that communicates with the chamber and has an insertion path into which a light guide member guiding light emitted from a light source is inserted,
• wherein, in a cross section including an axis of the needle tube and an axis of the insertion path, in a case in which a direction from the axis of the needle tube to a side on which the light introduction portion is located is a downward direction and a direction opposite to the downward direction is an upward direction, the inclined surface faces upward, a chamber-side opening of the insertion path is formed in a lower wall of the chamber, and the insertion path obliquely extends backward from the chamber-side opening in the downward direction,
• an upper wall of the chamber which is on a leading end side from the chamber-side opening is formed such that a height thereof gradually increases from the leading end to a rear end, and
• in a case in which the light guide member is inserted into the insertion path, is constrained at a first constraint point Y, becomes free, is bent, is constrained at a second constraint point X, and is inserted into the needle tube and a point where an extension line in an insertion direction of the light guide member in the vicinity of the chamber-side opening in the insertion path intersects a line which passes through the second constraint point X and is parallel to an axial direction of the needle tube is an intersection point A, a distance a between the intersection point A and the second constraint point X is longer than a distance b between the first constraint point Y and the intersection point A.