To provide a color divided plate printer for screen printing in which a color divided plate generating no Moire can be easily obtd. without repeating trial and error.

When a Moire confirming mode is designated (S1), a synthetic printing of four sheets of divided plate data, cyan, magenta, yellow and black is performed (S6) and then, synthetic printing of two plates are performed by laminating each divided plate data of each two colors (S7). When Moire is generated, it is confirmed from the result of the synthetic printing of four plates and it is confirmed which divided plate data the cause of Moire generation exists in from the results of the synthetic printings of each two plates.