A lens tube has two, first and second lenses (1, 2), a tubular lens frame (3) for holding the two lenses (1, 2), and three spacers (7) in contact with the opposite lens surfaces of the first and second lenses (1, 2). The spacers (7) are arranged so as to be in contact with curved surfaces of the first and second lenses (1, 2) and determine the distance between the first and second lenses (1, 2). The lens frame (3) has the same inner diameter between the first and second lenses (1, 2), and the spacers (7) are in contact with the inner wall of the lens frame (3). Since the lens frame (3) has the same inner diameter between the first and second lenses (1, 2), the first and second lenses (1, 2) are held with their centers perfectly aligned with each other.