brew: Homebrew must be run under Ruby 2.3! You're running 2.0.0

Any brew command I run (no matter brew update, brew -v), it gives me this error.

/Library/Ruby/Site/2.0.0/rubygems/version.rb:191:in `strip!': can't modify frozen String (RuntimeError)
	from /Library/Ruby/Site/2.0.0/rubygems/version.rb:191:in `initialize'
	from -e:1:in `new'
	from -e:1:in `<main>'
/usr/local/Homebrew/Library/Homebrew/brew.rb:12:in `<main>': Homebrew must be run under Ruby 2.3! You're running 2.0.0. (RuntimeError)

I know that there are some related issues with this, but after checking all of them, I still cannot find any solution to it.

Anyone can help with it?

Thank you.