A dual fueled diesel engine system with diesel fuel and reformed methanol has been investigated. Methanol can be reformed to reformed methanol (hydrogen 67% + carbon monoxide 33%) over suitable catalyst. The reformed methanol contains 20% more energy than methanol. Fundamental data of an electric heated reformer, performance of the dual fueled diesel engine to which hydrogen and carbon monoxide fed from gas bombs as a preliminary experiment, and then performance of the diesel engine with an onboard reformer were tested. In consequence, the feed of the reformed methanol improves the diesel engine performance.