The present study focuses on the effectiveness of negative and positive input on learning certain grammar rules which contain a learnability problem. In first language acquisition, the grammatical rules with a learnability problem are believed to be acquired through positive input alone with the help of the innate language acquisition device. In the second language acquisition, there are variant studies; some claim that positive input is effective just as it is effective in first language acquisition, and some claim that negative input is needed. The present study conducted the experiment in which Japanese learners were divided into three groups and each group was further divided into three groups accord-ing to their proficiency levels. One group was given instruction and correction (explicit negative input), another group was given instruction (implicit negative input), and the last group was given only sample sentences and no instruction (positive input). The results indicated that all the groups which received explicit negative input did better and so did some implicit negative input groups, whereas the positive input group did not make any significant progress. The advanced level group mostly made the most progress within the same input group.