In n page unit printing, a completion time of print preparation for page m+1 is estimated from the time spent for print preparation for pages up to page m among n pages. If the estimated time can make m+1 unit printing effective, print preparation for page m+1 is waited for. If the estimated time can not make m+1 unit printing effective, m page unit printing is immediately performed up to page m, without waiting for the completion of print preparation of page m+1.