1. A monitoring camera device comprising: an image capturer which captures an image of an object and generates a video image; a mask region storage which stores a mask region; a mask execution region setter which sets, as a mask execution region, a plurality of mask regions included in an image capturing range and defines a partial region to include at least two mask regions in the image capturing range, at least one mask region, set by the mask execution region setter, being outside of the partial region; a mask processor which performs mask processing on the mask execution region of the image capturer; and an image capturing range changer which changes the image capturing range of the image capturer; wherein the mask execution region setter changes a position of the partial region to include at least two mask regions based on a change of the image capturing region by the image capturing range changer, and selects, from the mask regions in the partial region, at least two mask regions positioned in the changed partial region from among the plurality of mask regions, based upon a predetermined criterion and the mask execution region setter generates an enlarged mask, smaller than the partial region, including the selected at least two mask regions and at least a portion of the partial region outside of the selected at least two mask regions, and sets the generated enlarged mask as the mask execution region; wherein the mask execution region setter defines a closeness evaluation value by multiplying a closeness value, representing a closeness of mask regions, with a weight coefficient and selects the at least two mask regions having a minimum closeness evaluation value, wherein the weight coefficient becomes smaller toward a side which is opposite to a side which is newly included in the image capturing range as a result of the change of the image capturing range or toward a side which is excluded from the image capturing range as a result of the change of the image capturing range.