Projection image generation method and magnetic resonance imaging device

An object of the invention is to reduce the operation required when generating a projection image from three-dimensional image data and to obtain a high-quality projection image regardless of operator's skill. To achieve this object, templates are prepared for each region and for each unnecessary tissue, the prepared templates are used according to a predetermined procedure, map processing is performed to specify the unnecessary tissue, and removal processing is performed to remove the region specified by the map processing. A function is also included in which three-dimensional image data before being processed is held and when the map processing and the removal processing produce undesired results, the results are recovered to the three-dimensional image data before being processed.