An objective of the present invention is to provide a dual curing type composite resin for core build-up, of which curing property by chemical polymerization is improved so that mechanical strength of a cured body can be improved under the condition of no light irradiation, and a setting time for clinical treatment can be shorten. The composite resin is composed of a first component including a (meth)acrylate polymerizable resin and an organic peroxide, and a second component including (meth)acrylate polymerizable resin and a reducing agent. A photopolymerizaton initiator and a filler are included in the first component and/or the second component, oxide powder of a Group II element in the periodic table having an average particle diameter of 1 µm or less is blended in the first component and/or the second component.
