The present invention relates to modality conversion for supporting Quality of Service (QoS) according to media resources, which includes the steps of receiving a modality conversion descriptor in which the characteristics of the modality conversion of the multimedia contents are described, receiving the multimedia contents, and converting the modality of the multimedia contents into a modality determined according to a media resource and the modality conversion descriptor. According to the present invention, a systematic approach to a design for an overlap content value model is provided so that the conversion boundaries between modalities can be quantitatively calculated. As a result, the correlation between various modalities can be established in a single model, and modality conversion supporting the optimal QoS can be performed.