An image pickup unit which consists of an objective optical system and a solid-state image pickup device: the objective optical system being composed of a first negative lens unit comprising a first meniscus lens element having a convex surface on the object side and negative power, a second positive lens unit comprising a convex lens element and an aperture stop disposed between the first lens unit and the second lens unit and this image pickup unit having a small outside diameter, allowing a field angle to be changed little due to variations of parts and an assembling variation, and having a maximum field angle of 150.degree. or larger.