Control of the translational motion of methyl radicals is demonstrated by using pulsed magnetic fields created by a series of solenoid coils. By synchronously switching the magnetic fields corresponding to the motion of the radicals, we have observed the deceleration and focusing of a supersonic radical beam. The present result shows that Zeeman deceleration of polyatomic free radicals in the doublet state can be realized. This opens possibilities for trapping cold polyatomic free radicals in a spatially confined area leading to further studies of cold collisions and reactions.