An ammonia-engine system is capable of supplying an ammonia cracking catalyst with a temperature necessary to promote a reaction even during low load operation in which a temperature of an exhaust gas from an ammonia engine is lower than an operating temperature of the ammonia cracking catalyst. In an ammonia-engine system provided with an ammonia engine (2) using ammonia as fuel and an ammonia cracking device (5) including an ammonia cracking catalyst that cracks ammonia and cracking ammonia to produce hydrogen, an ammonia oxidizing device (4) is provided between the ammonia engine (2) and the ammonia cracking device (5).
