A ceramic multilayer substrate includes a plurality of laminated ceramic layers and at least one conductor pattern and disposed on at least one of the ceramic layers. The ceramic multilayer substrate has a cavity in at least a first main surface. The ceramic multilayer substrate includes a deformation preventing pattern disposed on at least one of the ceramic layers having an opening forming the cavity. The deformation preventing pattern surrounds the entire perimeter of the opening and is made of the same material as the conductor pattern.