1. A monitoring device configured to monitor whether a look of a target person is in a proper state suitable for a working environment or a working content, the monitoring device comprising: an image input unit configured to input an image of the target person; a detector configured to analyze the image input by the image input unit and detect a predetermined region of a human body of the target person; a state estimator configured to estimate a state of the predetermined region detected by the detector; a proper state acquisition unit configured to acquire proper state information, the proper state information expressing a proper state of the predetermined region according to the working environment or the working content; and a controller configured to determine whether a present state of the predetermined region of the target person is proper by comparing an estimation result of the state estimator to the proper state information, and perform control according to a determination result, wherein the proper state acquisition unit is configured to analyze the image input by the image input unit, estimate the working environment or the working content of the target person, and decide the proper state of the predetermined region based on the estimation result of the working environment or the working content of the target person.