The present invention provides a medicament for treating a disease involving Nav 1.7 such as neuropathic pain, nociceptive pain, inflammatory pain, small-fiber neuropathy, erythromelalgia, paroxysmal extreme pain disorder, dysuria, and multiple sclerosis, which comprises a compound of formula (I): or a pharmaceutically acceptable salt thereof, wherein R 1a , R 1d , R 1c and R 1d are hydrogen, halogen, cyano, C 1-4 alkyl, C 1-4 alkoxy, or the like, provided that at least one of R 1a , R 1b , R 1c and R 1d is C 6-10 aryl, C 6-10 aryloxy, or the like, R 2 and R 3 are hydrogen, C 1-6 alkyl, C 3-10 cycloalkyl, or the like, R 4 is hydrogen, C 1-6 alkyl, C 3-7 cycloalkyl, or the like, m is 1, 2 or 3, L is CR 7 R 8 , and R 7 and R 8 are hydrogen, hydroxyl, C 1-4 alkyl, C 1-4 alkoxy, or the like.
