Yes definitely graduate level.
However I do not find this book offers a coherent passage through the subject at any level.
It contains chapters full of information, if you know what you are looking for, so is good as a reference, pretty much the main one in its field.
But I would not like to have to learn the subject from it, since the chapters seem rather disconnected.
In my view it is the sort of book that those who already know the subject say 'This is a good book' because it reminds them of what they already know (or half know).
So find a simpler auxiliary book until you are versed in the subject.