Aiming at effective perceptual training of second language learning, we carried out training experiments on Japanese geminate consonants. Native Korean learners were trained to identify geminate and singleton stop of Japanese. Since Korean language has no phonemic contrast between long and short consonants, learners have tried to learn their differences based on their categorical perception through training. To test the training efficiency and find generalization of temporal discrimination, we investigated the perceptual training with a word embedded in sentences and single/multiple speaking rate. Training experiments showed the superiority with a word embedded in sentences and multiple speaking rates. These results suggest that perceptual training which was trained by multiple speaking rates could be effective to perceive temporal discrimination of length contrast of Japanese. However, under the training stimuli was single speaking rate condition, perceptual training have generalized to the limited extent. These results suggest that context factors including speaking rate would affect to identify the length contrast of Japanese to L2 learners.