An image forming apparatus includes a medium reading section that acquires medium area data in a conveyance path, an image formation controller that sets a target pixel as a mask processing target where ink ejection is restricted when the target pixel is outside an image formable area, an anomaly estimation section that uses positions of a mask start pixel and a mask end pixel to estimate a cause of the mask processing target and generates a first text message indicating a result of estimation on the cause of the mask processing target, and an operation display section that, according to occurrence of the mask processing target, displays the first text message and an area as the mask processing target with a display generated using the position of the mask start pixel and the position of the mask end pixel superimposed on the image represented by the image data.