PURPOSE: To change a scale factor in a fine serration by letting a signal obtained by phase transfer be a video clock signal.

CONSTITUTION: This picture forming device is constituted so that a phase transfer part 116 switches (this switching is called the phase transfer) one of reference clock signals PH0 to PHn in conformity with the instruction of a phase transfer control signal from a compressing/expansion control part 118, and outputs the reference clock signal after the switching as the video clock signal DCK. Namely, when the phase transfer to the reference clock signal leading in its phase is performed, since the period of the video clock signal is compressed in proportion to the number of times of the phase transfer, a reducing function is obtained, and on the contray, when the phase transfer to the reference clock signal lagging in its phase is performed, since the period of the video clock signal is expanded in proportion to the number of times of the phase transfer, an enlarged function is obtained. In this case, the desired scale factor is set by performing the phase transfer of the prescribed number of times in accordance with the scale factor while keeping frequency constant.