A differential device is provided with: a ring gear having a tooth row arranged around an axis to mesh with an input gear; an outer case combined with the ring gear and rotatable about the axis; an inner case rotatable about the axis relative to the outer case and having a toothed end with axially projecting dog teeth; a differential gear set supported by the inner case and to be coupled with a pair of axles to allow differential motion between the axles; a clutch member engaging with the outer case and disconnectably connecting with the dog teeth so as to prevent the inner case from rotating relative to the outer case; and perforations penetrating the outer case and opened on an outer face of the outer case, the perforations being so disposed as to expose the dog teeth radially outwardly from the outer case.