Thank you for your advice and comment.
Firstly, I did not consider that frequency displayed on the commercial rigs is TX frequency even though frequency of uBitx is RX.
But I am still wondering why the difference of frequency between my ICOM transceiver and uBitx is 1.5Hz but not off set .
1.5KHz might be double of 700 or 800 Hz off set.
I think many uBitx user have been making the contact on CWL or CWU mode by uBitx.
So there is something I have not understood about offset of CW.
I would like to examine the cause of the frequency difference of 1.5KHz.