A pixel clock generator that is adapted to generate a pixel clock, the pixel clock generator comprising: a high frequency clock generator that is adapted to generate a high frequency clock; a comparator that is adapted to detect a time interval between a first synchronization signal and a second synchronization signal which are generated based on a light beam which is reflected by facets of a polygon mirror, compare the detected time interval with a target value, and output an error with respect to the target value; a frequency calculator that is adapted to calculate a set value of a pixel clock frequency based on the error output from the comparator, and output a frequency specification signal for specifying the pixel clock frequency based on the calculated set value; and a frequency divider that is adapted to divide the high frequency clock by a frequency division ratio based on the frequency specification signal output from the frequency calculator, and generate the pixel clock; characterized in that the frequency calculator includes a frequency-set-value storing unit that is adapted to store a plurality of set values of the pixel clock frequency, the set values including values for each facet of the polygon mirror; a set-value selecting unit that is adapted to select a set value by circulating the set values stored in the frequency-set-value storing unit for each of the first synchronization signal and the second synchronization signal; a frequency-specification-signal converting unit that is adapted to convert the set value selected by the set-value selecting unit into the frequency specification signal; and a set-value-calculation updating unit that is adapted to calculate the selected set value corresponding to the facet of the polygon mirror based on the error output from the comparator, and update the set value stored in the frequency-set-value storing unit, and the set-value-calculation updating unit is adapted to continue to calculate the set value corresponding to the facet until the error falls within a predetermined range and to update all the set values stored in the frequency-set-value storing unit with the set values that are calculated. a high frequency clock generator that is adapted to generate a high frequency clock; a comparator that is adapted to detect a time interval between a first synchronization signal and a second synchronization signal which are generated based on a light beam which is reflected by facets of a polygon mirror, compare the detected time interval with a target value, and output an error with respect to the target value; a frequency calculator that is adapted to calculate a set value of a pixel clock frequency based on the error output from the comparator, and output a frequency specification signal for specifying the pixel clock frequency based on the calculated set value; and a frequency divider that is adapted to divide the high frequency clock by a frequency division ratio based on the frequency specification signal output from the frequency calculator, and generate the pixel clock; characterized in that the frequency calculator includes a frequency-set-value storing unit that is adapted to store a plurality of set values of the pixel clock frequency, the set values including values for each facet of the polygon mirror; a set-value selecting unit that is adapted to select a set value by circulating the set values stored in the frequency-set-value storing unit for each of the first synchronization signal and the second synchronization signal; a frequency-specification-signal converting unit that is adapted to convert the set value selected by the set-value selecting unit into the frequency specification signal; and a set-value-calculation updating unit that is adapted to calculate the selected set value corresponding to the facet of the polygon mirror based on the error output from the comparator, and update the set value stored in the frequency-set-value storing unit, and the set-value-calculation updating unit is adapted to continue to calculate the set value corresponding to the facet until the error falls within a predetermined range and to update all the set values stored in the frequency-set-value storing unit with the set values that are calculated. a frequency-set-value storing unit that is adapted to store a plurality of set values of the pixel clock frequency, the set values including values for each facet of the polygon mirror; a set-value selecting unit that is adapted to select a set value by circulating the set values stored in the frequency-set-value storing unit for each of the first synchronization signal and the second synchronization signal; a frequency-specification-signal converting unit that is adapted to convert the set value selected by the set-value selecting unit into the frequency specification signal; and a set-value-calculation updating unit that is adapted to calculate the selected set value corresponding to the facet of the polygon mirror based on the error output from the comparator, and update the set value stored in the frequency-set-value storing unit, and the set-value-calculation updating unit is adapted to continue to calculate the set value corresponding to the facet until the error falls within a predetermined range and to update all the set values stored in the frequency-set-value storing unit with the set values that are calculated.