A capsule endoscope is disclosed that includes a light source, an objective optical system that forms an image of an object that is illuminated by the light source, an image pickup device that receives the image formed by the objective optical system; and a transparent cover that is positioned in front of the objective optical system. Specified conditions are satisfied by the objective optical system so that objects having a shape that conforms with the shape of the transparent cover at the periphery of the field of view, as well as more distant objects on-axis, are within the depth of field of the objective optical system's field of view. The transparent cover itself is purposely kept from being within the depth of field of the objective optical system's field of view.