It's a customized version of the PB-500F : the documentaion mentions an usual PD reference, here PD-131.
The machine is equiped with a 8kb RC8 ram card marked "n°11" with a calculation program in it and a corresponding manual in japanese.
The program is protected by a password : "K.M" (found thanks to Marcus tools).
Here it is
Written on the top : Estate
Written on the bottom : Mortages - national property fund loan