To provide a heavy oil ash combustion device, capable of re-utilizing heavy oil ash as the fuel of a coal fired boiler and contriving the effective utilization of natural resources.

A heavy oil ash combustion device is constituted, so that the device is provided with a heavy oil ash transferring device 80, transferring heavy oil ash collected by the electric dust collector 2 of a heavy oil fired boiler 1 by air, and a nozzle 90, causing the heavy oil ash, transferred by the heavy oil ash transferring device 80, to collide against coal layer in the outlet port unit of a coal feeder 60 to mix them, while the coal fed out of the coal feeder 60 from a coal banker 50, and the heavy oil ash produced by colliding the same against the coal to mix them, are crushed in a mill 70 so as to introduce them into the coal fired boiler 40 and to cause them to burn.