A form-fill-seal packaging machine produces a dummy bag from a film by starting to move seal jaws after the film has been pulled over a specified length or for a specified length of time from the moment when an eye mark on the film is detected by a detector. The voice command is determined to be a \u201cYes\u201d command when the low-frequency component precedes the high-frequency component; a \u201cStop\u201d command when the high-frequency precedes the low-frequency component and a \u201cNo\u201d command when the high-frequency component is below a predetermined threshold. The invention also relates to a method for correcting the step response. The light shielding plate is mounted between the light source and the lens.