Correlated electron oxide heterojunctions and their photovoltaic effect have attracted increasing attention from the viewpoints of both possible application to novel devices and basic science. In such junctions, correlated electron physics has to be taken into account in addition to conventional semiconductor modelling to explain distinctively emerging features. However, extracting novel functionalities has not been easy because it is not possible to predict their interfacial properties solely from their bulk characteristics. Here we describe a magneto-tunable photocurrent in a pn junction based on a correlated electron oxide La0.7Sr0.3MnO3 combined with a semiconducting SrTiO3 substrate. On applying an epitaxial strain, the photocurrent is enhanced threefold, which is increased 30% further by a magnetic field. Such a magneto-tunable effect is possible for only a narrow window of the correlated gap, which is itself adjusted by bandwidth and temperature. These results provide a guideline for utilization of correlated phenomena into the novel electronic devices.