This paper analyzes, from the politeness theory perspective, the current situation of the use of honorific-negative form, “~ません(か)”and “~ないです(か),” used by native Japanese speakers and Taiwanese Japanese learners in the exercise of request and refusal in Japanese conversations. The results of the study were as follows. (Ⅰ) this study found that the frequency of “ないです” was increased due to the lower D-value (social relationship) in the FTA. (II) this study found that native speakers used “ないです” more frequently when exercising “positive politeness” and “off-record strategy.” (Ⅲ) this study found the following reasons why learners used “ません” more often. Firstly, the learners’ awareness of using “ません” was quite strong when they were facing the superior. Secondly, the set phrase “ません(e.g., いただけませんか)” were used quite a lot, and furthermore, the learners were not aware of the fact that“ないです”would be used more in the positive politeness and off-record strategy.