1. An image reading method, comprising: a first moving step of moving one-dimensional image sensor over a first image in a first direction from a first position to a second position on opposite sides of said first image to thereby perform auxiliary scanning of said first image; during said first moving step, scanning said one-dimensional sensor in a direction non-parallel to said first direction to thereby perform main scanning of said first image; then, while said one-dimensional sensor is in said second position, changing said first image to a second image; then a second moving step of moving said one-dimensional sensor from said second position to said first position; and during said second moving step detecting reading conditions of said second image.