Abstract: A space monitoring system includes environment measuring means for measuring an atmospheric environment of a monitored space (S), person sensing means for sensing the existence of a person in the monitored space (S), space condition calculating means for calculating whether the monitored space is an indoor environment likely to cause droplet infection or whether the monitored space is expected to become an indoor environment likely to cause droplet infection, based on atmospheric environment data measured by the environment measuring means and person data sensed by the person sensing means, and display means for displaying an indication for facilitating a user to improve an existing indoor environment likely to cause droplet infection or prevent the monitored space from becoming an indoor environment likely to cause droplet infection, based on a result of calculation by the space condition calculating means.