The commutator method which was previously proposed for the purpose of calculating hindered matrix elements is applied to the Gamow-Teller beta matrix elements of heavier nuclei. It is shown that a number of empirical ft-values of the unfavored transitions can be well reproduced in terms of the conventional pairing model without invoking the phenomenological effective coupling constant. It is also shown that the l-forbidden transitions can be treated on the same footing as the unfavored ones. In such a treatment tensor forces play an important role. General forms of the effective single-body transition operators are derived on the basis of the commutator method, and qualitative discussions are given.