The present invention relates to a medicament for treating or preventing a disease involving Na channel, for example, neuropathic pain, nociceptive pain, inflammatory pain, small-fiber neuropathy, erythromelalgia, paroxysmal extreme pain disorder, dysuria, or multiple sclerosis, comprising a compound of formula (I) wherein R<；sup>；1a<；/sup>；, R<；sup>；1b<；/sup>；, R<；sup>；1c<；/sup>；, and R<；sup>；1d<；/sup>；are hydrogen, halogen, cyano, C<；sub>；1-4<；/sub>；alkyl, C<；sub>；1-4<；/sub>；alkoxy, etc., provided that at least one of R<；sup>；1a<；/sup>；, R<；sup>；1b<；/sup>；, R<；sup>；1c<；/sup>；and R<；sup>；1d<；/sup>；is the above C<；sub>；6-10<；/sub>；aryl, C<；sub>；6-10<；/sub>；aryloxy, etc., R<；sup>；2<；/sup>；and R<；sup>；3<；/sup>；are hydrogen, C<；sub>；1-6<；/sub>；alkyl, C<；sub>；3-10<；/sub>；cycloalkyl, etc., R<；sup>；4<；/sup>；is hydrogen, C<；sub>；1-6<；/sub>；alkyl, C<；sub>；3-7<；/sub>；cycloalkyl, etc., m is 0, 1, or 2, L is CR<；sup>；7<；/sup>；R<；sup>；8<；/sup>；, R<；sup>；7<；/sup>；and R<；sup>；8<；/sup>；are hydrogen, hydroxy group, C<；sub>；1-4<；/sub>；alkyl, C<；sub>；1-4<；/sub>；alkoxy, etc., or a pharmaceutically acceptable salt thereof.
