In this paper, we propose a method to generate a three-dimensional (3D) thermal map by overlaying thermal images onto a 3D surface reconstructed by a monocular RGB camera. In this method, we capture the target scene moving both an RGB camera and a thermal camera, which are mounted on the same zig. From the RGB image sequence, we reconstruct 3D structures of the scene by using Large-Scale Direct Monocular Simultaneous Localization and Mapping (LSD-SLAM), on which temperature distribution captured by the thermal camera is overlaid, thus generate a 3D thermal map. The geometrical relationship between those cameras is calibrated beforehand by using a calibration board that can be detected by both cameras. Since we do not use depth cameras such as Kinect, the depth of the target scene is not limited by the measurement range of the depth camera; any depth range can be captured. To demonstrating this technique, we show synthesized 3D thermal maps for both indoor and outdoor scenes.