This study investigated whether second language (L2) proficiency affects pragmatic comprehension, namely the ability to comprehend implied meaning in spoken dialogues, in terms of accuracy and speed of comprehension. Participants included 46 native English speakers at a U.S. university and 160 Japanese students of English in a college in Japan who were at different L2 proficiency levels. They took a 38-item computerized listening task measuring their ability to comprehend conversational implicatures of different types (i.e., 2 sets of items in different degrees of conventionality). The participants' comprehension was analyzed in terms of accuracy (i.e., test scores on a multiple choice measure) and comprehension speed (i.e., average time in seconds taken to answer each item correctly). The results revealed a significant L2 proficiency influence on accuracy, but not on comprehension speed. There was no significant relationship between accuracy and comprehension speed. A post hoc analysis of error data revealed a short-term memory influence on comprehension accuracy for L2 learners.