An image data rotating apparatus has an n.times.n dot matrix memory which temporarily stores n.times.n dots of image data supplied from a first image data memory. A row/column selector selects one row or column of the n.times.n dot matrix memory in response to a rotation indicating signal, which selects an integer times 90.degree. as a rotating degree, for example, 0.degree., 90.degree., 180.degree., 270.degree. or the like. The n dots of image data stored in the selected row or colum are re-written by outputting the stored data into a second image data memory, and by inputting another n dots of image data from the first image data memory in the same cycle, and with the repeating of this cycle, all the n.times.n dots of image data stored in the n.times.n dot matrix memory are re-written so that the rotated image data can be retrieved from the second image data memory.