1. A person detecting device comprising: a processor; and a memory having stored therein instructions that cause the processor to acquire, from a camera, a photographed image; determine, on the basis of a distance between a position of a first moving-object region extracted from a currently acquired image and a position of a second moving-object region extracted from an image acquired prior to the currently acquired image, a stationary region where a moving-object of the second moving-object region is in a stationary state; extract variations between feature quantities of images of stationary regions having been stored for the stationary regions and a feature quantity of the currently acquired image; and determine presence or absence of a person in the stationary region using the extracted variations, wherein the stationary region is determined to include a person when the variation is within a predetermined range.