Cross-laminated timber (CLT) has received particular attention as a structural material, and its material and joint strengths have been researched. This study derived a strength formula for dowel-type CLT joints with slottedin two steel plates, based on Johansen’s yield theory. When the steel plate is inserted in CLT that has five laminae, the dowel-type joints with slotted-in two steel plates have thirty-nine yield modes. This study derived the formulas for each yield mode and compared them with experimentally obtained results. The yield mode assumed by the yield theory was congruent with the failure mode of the CLT specimens after the experiments. The strength of dowel-type joints calculated based on the yield theory was close to the yield strength obtained in the experiments.