To provide a cutting jig for a ceiling cornice for cutting easily an end face at 45° easily.

A cutting jig 2 for a ceiling cornice 1 is formed into almost the trapezoidal sectional shape and both oblique sides of the trapezoidal shape cross each other orthogonally, and the cutting jig is used for cutting an end face of the ceiling cornice 1 with one oblique side forming a ceiling setting face 11 and the other oblique side forming a wall setting face 12 at an angle of 45° in the longitudinal direction in the plan view, and the cutting jig is formed of a hollow square cylindrical body for bringing the ceiling setting face 11 and the wall surface setting face 12 of the ceiling cornice 1 into contact with the inner peripheral face of the jig and inserting them into the body, and at least the end face of one side is formed into a cut edge 21 at 45° in the longitudinal direction in the plan view.