An image sensor module includes a holder and a lens unit attached in the holder. The lens unit is held in the holder by at least one engagement projection formed by plastically deforming a part of the holder. Preferably, the lens unit includes a first lens spaced from the engagement projection and a second lens adjoining the engagement projection. Each of the first lens and the second lens includes a central lens portion, and a flat peripheral portion surrounding the lens portion. The flat peripheral portion of the first lens is held in contact with the flat peripheral portion of the second lens. The engagement projection engages the flat peripheral portion of the second lens.