A focusing apparatus includes a first sensor and a second sensor configured to receive an optical image of a target workpiece to be inspected and convert it photoelectrically, a first optical system configured to make the optical image be focused on the first sensor, a second optical system configured to branch the optical image from the first optical system and to make a branched optical image be focused on the second sensor, a focus detection part configured to input a first image signal photoelectrically converted by the first sensor and a second image signal photoelectrically converted by the second sensor and to detect a focus position of the optical image by using high frequency components of the first image signal and the second image signal, and a focus control part configured to control a focus of the first optical system based on the focus position detected by the focus detection part.