Freezing behavior is frequently observed among forest-dwelling ungulates and is thought to function as a method of concealment from predators. However, because of the difficulty of observing such behaviors, detailed observations have not previously been conducted to provide evidence for this interpretation. Therefore, we have examined the response to human observers of the Japanese serow (Capricornis crispus), a typical forest dweller, in relation to visibility and group size based on direct observations conducted over 3 years. From a total of 221 sightings, freezing behavior was observed more frequently in the closed habitat (14.3% of 196 sightings) and during the growing season (22.8% of 92 sightings) than in the open habitat (0% of 25 sightings) and during the non-growing season (5.2% of 129 sightings). Freezing behavior was also frequently observed in solitary animals (15.2% of 184 sightings) than in groups (0% of 37 sightings). These results suggest that the function of this freezing behavior is concealment from predators. Japanese serows fled more frequently in the open habitat (72%) and during the non-growing season (58.7%) than in the closed habitat (18%) and during the growing season (41.3%). Japanese serows selected closed habitat significantly more often regardless of the season. These results suggest that Japanese serow adopt cryptic anti-predator strategy to avoid detection by predators in the dense forest habitat, and their strategy changes according to visibility.