A distortion correcting apparatus includes a buffer circuit which writes image data having horizontal pixels of a first number and a vertical-distortion different depending on a horizontal pixel position, into an SDRAM. The written image data is read-out for each units of horizontal pixels, which include a reference horizontal pixel and indicates a second number smaller than the first number, in a vertical pixel direction. A buffer control circuit in the vertical-distortion correcting circuit determines a second number in such a manner as to indicate a larger numerical value as a vertical-distortion corresponding to the reference horizontal pixel is smaller so as to start the buffer circuit. Also, the buffer control circuit changes a position of the reference horizontal pixel to a position corresponding to the second number at a timing based on a correction amount of the vertical-distortion correcting circuit so as to start the above-described determining process.