There is provided a mounting structure of a mounted component, including: a holding member that holds a mounted component including a light source and of which position is adjusted within a plane substantially orthogonal to an optical axis of the light source; a shaft portion that projects from a side surface of a case body in which the light source is provided, in a direction along the optical axis of the light source; and a fixing member in which a contact portion coming into contact with the shaft portion is provided, wherein in a state in which the contact portion contacts the shaft portion, rotation of the fixing member is limited in an allowable range, and the fixing member is made to adhere to a surface of the holding member facing toward the fixing member in the direction along the optical axis, and is fixed to the shaft portion.