Domestic

http://www.jal.co.jp/en/dom/baggage/inflight/

International

http://www.jal.co.jp/en/inter/baggage/inflight/

So basically you will be one item over the allowamce for all of your flights. JAL is not big on policing the limits, but then again people are generally not dragging their life's belongings on board. So generally it works out pretty well.

A main thing being, JAL luggage delivery is super efficient even at out stations.