A printer for printing on a medium on an endless belt by printer heads includes: a generator generating printing data for each printer head; a detector detecting time-series data for the meandering of the medium; a generator generating correction data preventing disorder of a printed image due to the meandering; and a controller operating each printer head according to the correction and printing data, wherein the correction-data generator selects a specific difference between factors in the time when the time-series and predetermined time-series data are related and newly generates correction data corresponding to the selected factor, wherein a replacement section replaces a factor in the time corresponding to the specific factor of the reference time-series data with the specific factor, and the time-series-data detection section detects the time-series data when power is supplied to the printer.