To widen an angle of view and make an image surface coincide with the neighborhood of an image pickup surface over the whole angle of view. A capsule endoscope 10 includes an image pickup optical system 20 for capturing an image of an object surface 12 in the shape of concave hemisphere surface. The image pickup optical system 20 satisfies a condition expressed by -5‰¤ ”Zr/”Zp ‰¤5. Here, when a maximum half angle of view is Émax, ”Zr denotes a difference between a position of a real image surface with respect to light flux of 2Émax and that with respect to light flux of É max, and ”Zp denotes a difference between a paraxial image forming position of a virtual object plane surface 24 and that of a virtual object plane surface 25. The virtual object plane surface 24 passes through an intersection point P1 of the object surface 12 and principal rays of 2 É max, and is vertical to an optical axis XP. The virtual object plane surface 25 passes through an intersection point P2 of the object surface 12 and principal rays of Émax, and is vertical to the optical axis XP.
