An image generating apparatus capable of facilitating analysis of a substance having a repeating structure has: an ion intensity data acquisition portion for acquiring ion intensity data arising from the substance, the data including information about a relative intensity of each ion against mass-to-charge ratio; a mass information acquisition portion for acquiring mass information about the repeating unit of the substance; a data alignment portion for aligning the ion intensity data within each given range of mass-to-charge ratios based on the mass information about the repeating unit of the substance; and an image generation portion for generating an image based on the aligned ion intensity data.