The present invention provides an inertia test apparatus for a model ship that mimics a pitching inertia radius of an actual ship by reciprocating a model ship. The apparatus includes a base frame providing a supporting force, vertical frames integrally fixed at both sides of the base frame and having a hinge shaft on an upper end, a swing including a pair of fixing members rotatably hung on the hinge shafts of the vertical frames and a bed integrally formed at a lower ends of the fixing members, and providing a pitching inertia radius of the model ship by reciprocating about the hinge shafts, with the model ship seated on the bed, and a centering adjuster seating the model ship on the bed of the swing and matching a center of gravity of the model ship with a center of the swing by allowing the model ship to move.