I can not enter '\' when type alt+\

[Hiromu SAKAMOTO]

Hello
My name is Hiromu SAKAMOTO
I use Lyx 2.1.2.1 on yosamite with jis keyboad.
However I can not enter '\' when I type alt + '\'.
Please tell me how to enter '\'.

hiromu_sakam...@pop11.odn.ne.jp