1. A charged particle beam apparatus comprising: a charged particle beam column configured to irradiate a charged particle beam to a first region and a second region of a sample, the second region included in the first region; a controller configured to control the charged particle beam column to irradiate the charged particle beam to the first region and the second region of the sample, the first region including a plurality of first pixels at a first pixel interval, each of the first pixels including a first predetermined number of first sub-pixels, the second region including a plurality of second pixels at a second pixel interval different from the first pixel interval, each of the second pixels including a second predetermined number of second sub-pixels, wherein the controller is configured to control the charged particle beam column to irradiate the charged particle beam to each of the first sub-pixels at the first pixel interval for the first region and to irradiate the charged particle beam to each of the second sub-pixels at the second pixel interval for the second region; a secondary electron detector configured to detect first secondary electrons for each of the first sub-pixels generated by irradiating the charged particle beam to each of the first sub-pixels at the first pixel interval for the first region, to generate a first signal of the first secondary electrons for each of the first sub-pixels, to detect second secondary electrons for each of the second sub-pixels generated by irradiating the charged particle beam to each of the second sub-pixels at the second pixel interval for the second region, and to generate a second signal of the second secondary electrons for each of the second sub-pixels; and an image forming unit configured to form first sub-pixel images by using the first signal, the number of the first sub-pixel images being the first predetermined number, to generate a first image by synthesizing the predetermined number of the first sub-pixel images, and to form second sub-pixel images by using the second signal, the number of the second sub-pixel images being the second predetermined number, to generate a second image by synthesizing the predetermined number of the second sub-pixel images.