A light source unit is characterized by including a light source (46) including a light emitting portion (48), a light source holding member (52) holding the light source (46), a light transmission member (36) including an incident portion (37) wherein light from the light emitting portion (48) is to enter the incident portion (37), a light transmission member holding member (58) holding the light transmission member (36), a positioning portion (70a 70b) provided on the light transmission member holding member (58) and abutted on the light source (46) to position the light transmission member holding member (58) and the light source (46) to position the incident portion (37) and the light emitting portion (48), and an adjustment joining mechanism (56a, 56b, 74a, 74b, 75a, 75b, 76a, 76b, 78, 80a, 80b) configured to join the light transmission member holding member (58) and the light source holding member (52) to each other so as to adjust the relative positions of the light transmission member holding member (58) and the light source holding member (52), and joining the light transmission member holding member (58) and the light source holding member (52) to each other in a state where the light source (46) and the positioning portion (70a 70b) abut on each other.
