The set \(\mathcal {C}\) of complex-valued continuous functions on \([0,\infty )\) is a ring for addition and convolution. It has the quotient field \(Q(\mathcal {C})\) , by which J. Mikusiński developed his operational calculus. In this paper, we revisit a derivation and a transforming operator for \(Q(\mathcal {C})\) discussed in his textbook, and define a new transforming operator related to the q-shift operator, which gives structures of a q-difference field and a difference field of Mahler type to \(Q(\mathcal {C})\) .