The invention provides a starting method and starting device for internal combustion engine to easily break down the top dead center of initial compression after the release of decompression operation, while avoiding the upsizing of an electric motor for starting. In an internal combustion engine having a decompression mechanism, a decompression cam rotatable, in relation to a camshaft in the angle Ad between a first and second stop positions, has a cam profile such that an exhaust valve is in an opening state at the first stop position and in a closing state at the second stop position. At engine start (position P1), the decompression cam is rotated in reverse to locate at the first stop position by reversely rotating a crankshaft with the electric motor, and after the crankshaft only is further rotated reversely (position P3), the decompression cam is rotated positively, by positively rotating the crankshaft with the motor. During the decompression cam reaches the second stop position, it makes the exhaust valve in the opening state to enlarge a crankshaft runup angle in either one of compression stroke (S8, S12) included in the range of reverse rotation angle Ar or an initial compression stroke, after starting the positive rotation of decompression cam. |