  An x-ray detector for a solar axion search was developed. The detector is
operated at 60K in a cryostat of a superconducting magnet. Special care was
paid to microphonic noise immunity and mechanical structure against thermal
contraction. The detector consists of an array of PIN photodiodes and tailor
made preamplifiers. The size of each PIN photodiode is $11\times 11\times 0.5\
{\rm mm^3}$ and 16 pieces are used for the detector. The detector consists of
two parts, the front-end part being operated at a temperature of 60K and the
main part in room temperature. Under these circumstances, the detector achieved
1.0 keV resolution in FWHM, 2.5 keV threshold and 6\times 10^{-5} counts
sec^{-1} keV^{-1} cm^{-2} background level.
