  To clarify superconductivity in EuFe2As2 hidden by antiferromagnetism of
Eu2+, we investigated a Ca-substituted sample, Eu0.5Ca0.5Fe2As2, under high
pressure. For ambient pressure, the sample exhibits a spin-density-wave (SDW)
transition at TSDW = 191 K and antiferromagnetic order at TN = 4 K, but no
evidence of superconductivity down to 2 K. The Ca-substitution certainly
weakens the antiferromagnetism. With increasing pressure, TSDW shifts to lower
temperature and becomes more unclear. Above 1.27 GPa, pressure-induced
superconductivity with zero resistivity is observed at around Tc = 20 K. At
2.14 GPa, Tc reaches a maximum value of 24 K and the superconducting transition
becomes the sharpest. These features of emergence of the superconductivity are
qualitatively similar to those observed in AFe2As2 (A = Ba, Ca).
