The invention provides a mechanically-fired boiler. The mechanically-fired boiler comprises a boiler body, a combustion chamber and a feed device. The combustion chamber is arranged in the boiler body. A chain fire grate is arranged below the combustion chamber. The feed device is used for supplying fuel into the combustion chamber through a feed port in the boiler body. One end of the chain fire grate extends out of the boiler body from the position of the feed port. According to the above mechanically-fired boiler, because one end of the chain fire grate extends to the exterior of the boiler body from the position of the feed port and extends out of the boiler body, the fuel can be driven by the chain fire grate to automatically enter the combustion chamber in the boiler body through the feed port to be combusted only by directly placing bulk or non-bulk solid fuel on the portion, extending out of the boiler body, of the chain fire grate, no feed structures for pushing the solid fuel into the feed port need to be specially arranged, the structure is simple, cost is saved, the feed efficiency is high, and the solid fuel large in size can easily enter the mechanically-fired boiler.