The present study attempted to confirm the validity of the Foreign Language Grammatical Carefulness Scale (FLGCS) developed by Kusanagi et al. (2015). According to Kusanagi et al. (2015), Grammatical Carefulness (GC) is defined as a personal trait reflecting learners’ behavioral and psychological aspects of language use, and it consists of three subscales: phonological carefulness, lexical-syntactic carefulness, and pragmatic carefulness. Although the initial validation concerning factorial, content, and criterion-based validity has been done, the criterion-based validation did not take into account the correlation between the performance focusing on the specific aspects of language use and each subscale under the GCS. In order to examine the validity of the subscales of GCS, this study applied two types of task: a discourse completion task (DCT) and a reading and underlining task (RUT), which are considered to measure pragmatic and lexical-syntactic aspects of learners’ performance respectively. It was found that the two subscales (lexical-syntactic and pragmatic) and the scores of the two tasks were weakly correlated, which means that this study found additional evidence showing the validity of FLGCS.