A target device 20 includes: a prism 22 configured to reflect light incident on the prism in a direction identical to a direction of incidence of the light; a support part 21 configured to support the prism 22; and a plurality of direction indicators 23 formed on the prism 22 to indicate a direction of the prism. A surveying system 1 includes the target device 20 attached to a camera 11 of a UAV 10, and a surveying device 3 surveying the prism 22 as a target and taking a target image Tp including the prism 22 to detect the orientation of the UAV 10 based on the direction indicators 23 appearing in the target image.