An object of the present invention is to provide a dimension measurement device with the ability to accurately determine a size of a measurement object, a parcel locker system including such a dimension measurement device, and a dimension measurement method. A dimension measurement device (101) according to the present invention includes: a storage receptacle (111); an imager (103) configured to capture an image of a measurement object (150) to be stored in the storage receptacle (111); and an image processor configured to process the image captured by the imager (103). The storage receptacle (111) includes: a rectangular lower surface (1201); a rectangular first side surface (1242); and a rectangular second side surface (1232). The storage receptacle (111) further includes: a first concave corner (112) formed by the lower surface (1201) and the first side surface (1242); a second concave corner (113) formed by the lower surface (1201) and the second side surface (1232); and a third concave corner (114) forme
