A structure of an imaging part in a catheter is provided that is capable of easily enlarging the angle of view, and moreover hinders the ingress of surrounding debris and fluids such as bodily fluids into the space between the object lens system and the light receiving surface of the solid state imaging element. For that reason, the structure of an imaging part has an object lens system in which light from an observation object region is incident; and a solid state imaging element for receiving an outgoing light from the object lens system and photoelectrically converting an image of the observation object region, in which at least a lens face of a light outgoing side of the object lens system is formed to be planar, and the lens face of the light outgoing side of the object lens system is joined to the light receiving surface of the solid state imaging element.