A maintenance information output apparatus which can output maintenance information of a speed reducer more adequately than the prior art is provided.A maintenance information output apparatus 130 has: an operating portion 131 which is operated by the user; a wired communicating portion which receives data of an amount of iron from an iron amount detecting device that is attached to a speed reducer 20 of an industrial robot 10, and that detects the amount of iron in a lubricant in the speed reducer 20, through a portable wireless receiver 120; a hard disk which stores the data of the amount of iron received by the wired communicating portion; a display 134 which outputs maintenance information of the speed reducer 20; and a processing device which is configured by a CPU, a ROM, a RAM, and the like, and which controls the operations of the wired communicating portion, the hard disk, and the display 134 in accordance with an operation on the operating portion 131. When the amount of iron in the lubricant in the speed reducer 20 is equal to or larger than a threshold value, the processing device causes the display 134 to output maintenance information.