An endoscope apparatus includes an objective optical system mounted at a distal end portion of an endoscope, which is inserted into a tube cavity, and configured to form an image of an object in the tube cavity, the objective optical system including a focusing lens movable in an optical axis direction, a solid-state image pickup device for color image pickup configured to pick up the image formed by the objective optical system, a color separation filter being arranged for each pixel in the solid-state image pickup device, a focus adjusting mechanism configured to move the focusing lens and automatically adjust the objective optical system to a focus position in a focused state, etc. wherein, when the objective optical system is automatically adjusted to a focus position by the focus adjusting mechanism, resolving power equal to or larger than 35 µm is obtained at a focus position where a distance between the objective optical system and the object is equal to or smaller than 15 mm and, when a range in which MTF of a spatial frequency 1/(3 × P) is equal to or higher than 10% is defined as width of depth of field, the objective optical system has width of depth of field equal to or larger than 5 mm.
