A cap mountable on and detachable from an intraoral scanner including a housing having an opening for connecting to at least a part of the intraoral scanner, a measurement window provided in the housing and located opposite to the opening, and a mirror that reflects light from the measurement window toward the opening. The housing has a longitudinal length shorter than that of a probe defining a depth-of-field, of the intraoral scanner extending from the measurement window to a predetermined extent.