A monitoring device and A monitoring method of the invention provide a technique for more simply generating information on people in a monitored target space. The monitoring device (1) according to the invention includes: an image acquisition unit (10) that acquires unit thermal images (40_1 to 40_x) from thermal image sensors (4_1 to 4_x); an image processing unit (11) that generates thermal image data (150) representing two-dimensional temperature distribution of a monitored target space based on the unit thermal images acquired by the image acquiring unit; a maximum temperature calculation unit (12) for calculating a maximum temperature for each pixel of the thermal image sensors based on the thermal image data; a minimum temperature calculation unit (13) that calculates a minimum temperature for each pixel based on the thermal image data; and a difference temperature calculation unit (14) that calculates a difference between the maximum temperature and the minimum temperature for each pixel.