Ink-jet printing apparatus and preliminary discharge control method for the apparatus

An ink-jet printing apparatus which comprises a plurality of printing heads, each having an array of ink discharging elements, and prints by discharging ink from the elements onto a printing medium, comprising:

• preliminary discharge performing means for performing, a predetermined number of times, driving of the elements of one printing head in performing preliminary discharge of ink unrelated to printing;
• printing head switching means for switching, in a predetermined cycle, the one printing head for which the preliminary discharge is to be performed to at least one other printing head;
• and
• control means for controlling said preliminary discharge performing means and said printing head switching means so as to perform the preliminary discharge the predetermined number of times for all the elements of the plurality of printing heads by repeating the predetermined cycle a plurality of times,
• wherein the predetermined cycle includes a cycle corresponding to a maximum frequency at which each printing head can be driven.