  The Hamiltonian of persistent current qubit is found within well known
quantum mechanical procedure. It allows a selfconsistent derivation of the
current operator in a two state basis. It is shown that the current operator is
not diagonal in a flux basis. A non diagonal element comes from the finite
inductance of the qubit. The results obtained in the paper are important for
the circuits where two or more flux qubits are coupled inductively.
