1. An endoscope apparatus comprising: a light source unit that is capable of adjusting quantity of light and irradiates illumination light to a subject; an imaging element that captures a captured image by return light from a living body that is the subject in the illumination light and outputs a captured image signal; a brightness calculating section that calculates a value of brightness of each pixel of the captured image on basis of the captured image signal; and an image processing section that performs a predetermined image processing on the captured image, wherein the light source unit includes: a first light source section that emits broadband light having a wide wavelength band including a visible region, a second light source section that emits narrowband light having a wavelength bandwidth narrowbanded according to spectral characteristics of the structure and components of the living body used as the subject, and a light source control section that controls light emission, irradiation light quantity, and a light quantity ratio from the first light source section and the second light source section, wherein the image processing section includes a frequency band enhancing section that applies a predetermined frequency band filter to the captured image, and wherein the frequency band enhancing section determines whether a value of brightness of a particular region of the captured image is either larger or smaller than an average value of the brightness of pixels of the captured image or a reference value provided in advance, whereby when the value of brightness of the particular region is larger than the average value or the reference value, an enhancement degree of the frequency band filter is strengthened, and when the value of brightness of the particular region is smaller than the average value or the reference value, the enhancement degree of the frequency enhancing filter is weakened.