Disclosed herein are an additional information superposition method and a video signal outputting apparatus, wherein the additional information superposition method for superposing additional information spectrum spread with spread codes synchronized with a vertical synchronizing signal on a second video signal for forming an image of an aspect ratio of N:n which is to be converted into and outputted as a first video signal for forming an image of another aspect ratio of M:m, comprising the steps of setting a size of a unit block before conversion in the second video signal based on a size of a unit block after conversion to which one chip of spread codes for despreading determined in advance is allocated and contents of a conversion process into the first video signal, and superposing the additional information spectrum spread with the spread codes of one chip allocated for each unit block before conversion having the set size in such a manner as to allow the additional information to be extracted from the first video signal.