1. A multimedia contents converting apparatus, comprising: a text display time calculation processing unit being configured to calculate an adjusted display time period of text media to be included in output multimedia contents on the basis of conversion instruction information; a spatiotemporal layout information setting processing unit being configured to set spatiotemporal layout information on said output multimedia contents on the basis of said conversion instruction information; and a contents conversion processing unit being configured to convert input multimedia contents, including text media and media other than the text media, oriented to a personal computer to be displayed on a screen of the personal computer with a predetermined size into said output multimedia contents oriented to portable terminal to be displayed on a screen of the portable terminal with a size smaller than said predetermined size on the basis of said spatiotemporal layout information, wherein said spatiotemporal layout information setting processing unit is configured to set a display time period of said text media included in said spatiotemporal layout information, on the basis of said display time period of said text media calculated in said text display time calculation processing unit, and modify and synchronize a playing time period of said media other than said text media included in said spatiotemporal layout information, responsive to said display time period of said text media set as said spatiotemporal layout information.