A printer printing an image on a print medium based on print data including print dot data for each of print lines. The printer includes a print head including heating elements arranged along a direction of the print lines, and a controller finding the number of print dots on each print line and determining a first or second control mode as a control mode of the heating elements for printing each print line based on the found number of print dots. In the first control mode, the heating elements are divided into first groups including two or more adjacent heating elements and are heated at a different timing. In the second control mode, the heating elements are divided into second groups including two or more heating elements with at least two thereof spaced apart and are heated at a different timing.