This paper introduces an easy method for the fabrication of a diaphragm micropump using an ionomer-based polymer actuator. The polymer actuator was fabricated by electroless plating of platinum onto a Nafion-117 film. The electrode that serves as the diaphragm has a simple circular shape without any modification of the electrode surface and was punched from the polymer actuator film in a single step. The whole body of the micropump was designed to be the size of a credit card and was fabricated by the lamination of 13 layers to construct a three-dimensional flow path inside the body. The actuator assembly was embedded at the bottom of the pump to facilitate the exchange of the diaphragm. A square polarization waveform with amplitudes of +2.0 V and −2.0 V was applied to the pump, and the diaphragm micropump transported water at ∼5 μL/s with no water leakage. The results presented in this work are an important demonstration that a diaphragm micropump can be easily fabricated for many micro-total analysis system (micro-TAS) applications using the nature of an ionomer-based polymer actuator as a flexible and large deformation available property in aqueous media.