Comics are entertainment contents that conversations of characters drive stories. Since people can obtain new knowledge from conversations in real lives, the conversations in comics could be useful to acquire new knowledge. The conversations in comics contain various utterance sentences of characters. Some of the utterance sentences contain knowledge, and the others not. We define the utterance sentence as a knowledge explanation sentence. If the knowledge explanation sentences are extracted automatically, those can be used for knowledge acquisition with comics and comics recommendation.In this paper, we propose an extraction method of the knowledge explanation sentences from characters’ conversations in comics. We assume that the knowledge explanation sentences include content words and expressions that are special for knowledge explanation. The proposed method represents a sentence as a combination vector of an averaged word vector and an expression vector. The averaged word vector is an average of each content word’s embedding. The expression vector has factors of expression meanings that are used for knowledge explanation. The combination vectors are trained by Support Vector Machine to obtain a classifier. The classification outputs a set of knowledge explanation sentences that will be an extraction result.We tested the proposed method by comparing other methods with 4,611 sentences from five comics. The proposed method obtained 0.80 accuracy, 0.77 precision, and 0.88 recall that were the highest among the prepared methods.