In this study, we numerically investigated the blockage effects on shock-induced motion of a solid body in a shock tube with a rectangular cross-section. By utilizing the overset grid functionality of an open source CFD (Computational Fluid Dynamics) software, OpenFOAM® v1712, we simulated the motion of a cuboidal solid body with six degrees of freedom induced by an impingement of a planar shock wave with a propagating Mach number of 1.3. The simulations were conducted for three-dimensional inviscid flows in shock tubes with widths ranging from 30 to 100 mm. We compared several outcomes from the simulations with varying shock tube widths. These include computational shadowgraph images, the time histories of the translational and angular displacements of the solid body, and those of the aerodynamic force and moment exerted on the solid body. It was found that under the present conditions, the drag force acting on the solid body during a quasi-steady state created after the shock passage decreased with the width of the shock tube. In contrast, the pitching moment exerted on the solid body was not significantly affected by the width of the shock tube.