Abstract: A bag making machine for manufacturing bags from an elongated film having print patterns repeatedly printed on one surface or two surfaces at a print pitch corresponding to a predetermined number of bags includes a processing unit configured to process the film for each length corresponding to the predetermined number of bags, a moving mechanism configured to move the processing unit, a shooting device, and an image processing device. The shooting device includes not less than one line sensor installed with a longitudinal direction of the line sensor extending along the widthwise direction of the film and obtains a linear image extending throughout a width of the film for each shooting operation. The image processing device sequentially receives the linear images from the shooting device and detects the actual length of the predetermined number of bags of the film based on an image extending throughout the width of the film.