thank you for your advice...
But with LiAlH4 we commely use a non protic solvent.
However for NaBH4 we could use MeOH. I have tried to put a large quantity of NaBH4 in MeOH, without any other reagent... And it react.. Slowly at first, then I clearly saw hydrogen bubles! So I wonder if , actually, there is not a generation of HxB(OMe)4-x which react with the carbonyle. But also, the first proposition, which some BH4 directly react with carbonyle.