Present status of the development of superconducting tunnel junctions for the detection of X-ray photons and heavy ions is reported. The energy resolution for 5.9 keV X-rays was measured to be 41 eV, 58 eV, 65 eV and 129 eV with STJs of 2020 µm2, 100100 µm2, 200200 µm2 and 500500 µm2, respectively, and a model to describe the phonon-mediated X-ray signals is discussed. Direct voltage switching induced by heavy ions was successfully observed.