1. An object detection device comprising: a binary difference image generation unit for generating a binary difference image by binarizing a difference value, with a predetermined threshold for the difference value, between: a background image which is an image showing a temperature distribution in a detection area and which is an image as a reference for the absence of a detection target object in the detection area; and a detection target image which is an image showing a temperature distribution in the detection area and which is an image as a detection target to detect a detection target object in the detection area; a binary second derivative image generation unit for generating a binary second derivative image by binarizing second derivatives of the detection target image or of a smoothed image, obtained by smoothing the detection target image, with a predetermined threshold for the derivative; and an object detection unit for detecting the detection target object based on a logical product of the binary difference image and the binary second derivative image.