1. An endoscope system comprising: an objective optical system that is provided at an insertion portion tip and that acquires a subject image; an optical path division means for dividing the subject image into two optical images with different focuses; an imaging element that forms the two optical images with different focuses at the same time to acquire two images; an image correction means for correcting the two images acquired by the imaging element so that differences other than the focuses become substantially the same; and an image combination processing unit that selects an image with a relatively high contrast in predetermined corresponding areas between the two images corrected by the image correction means to generate a combined image, wherein the optical path division means is a polarization beam splitter, and a crystal filter including a crystal shaft forming 45 degrees relative to an incident surface of the polarization beam splitter is arranged on an object side of the polarization beam splitter.