1. An image capturing apparatus comprising: an image capturing section; a pre-image acquiring section for acquiring a pre-image captured by the image capturing section when a focal point provided at a predetermined position within the image capturing region of the image capturing section is superimposed on a main subject; a focal distance adjusting section for adjusting a focal distance of the image capturing section to the main subject based on an analysis result of the pre-image acquired by the pre-image acquiring section; a captured image acquiring section for acquiring the image captured by the image capturing section when the image capturing section focuses on the main subject; a focal position storage section for storing a focal position on an image capturing range of the image capturing section; and an image storage section for storing a region image including the focal position stored in the focal position storage section in the pre-image acquired by the pre-image acquiring section in a nonvolatile memory in association with the captured image acquired by the captured image acquiring section, further comprising an instruction input button for causing the pre-image acquiring section to acquire the pre-image through half-pushing by a user and causing the captured image acquiring section to acquire the captured image through full-pushing by the user, wherein: the pre-image acquiring section acquires the pre-image captured by the image capturing section by half-pushing the instruction input button, the focal distance adjusting section adjusts the focal distance to the main subject on which the focal point is superimposed based on the analysis result of the pre-image acquired by the pre-image acquiring section, the captured image acquiring section acquires the image captured by the image capturing section after the image capturing section adjusts the focal distance to the main subject by full-pushing the instruction input button the image acquiring section acquires a plurality of pre-images captured by the image capturing section every time the instruction input button is half-pushed, the focal distance adjusting section adjusts the focal distance to the main subject on which the focal point is superimposed based on the analysis result of the pre-image acquired by the pre-image acquiring section every time the instruction input button is half-pushed, the focal position storage section stores the focal position on the image capturing range of the image capturing section which is adjusted by the focal distance adjusting section every time the instruction input button is half-pushed, the image capturing section determines an image capturing condition based on the plurality of focal distances adjusted by the focal distance adjusting section every time the instruction input button is half-pushed in the case that the instruction input button is half-pushed several times, the captured image acquiring section acquires the image captured by the image capturing section after the image capturing condition is adjusted to the image capturing condition determined by the image capturing section through full-pushing the instruction input button, and the image storage section stores the region image including the focal position stored in the focal position storage section in each of the plurality of pre-images acquired every time the pre-image acquiring section half-pushes the instruction input button in the nonvolatile memory in association with the captured image acquired by the captured image acquiring section.