X-ray spectroscopy of hadronic atoms is a powerful method
to determine the strong interaction between the hadron and
nuclei. At J-PARC, we have conducted two experiments on
exotic atoms with a doubly strange hyperon, $\Xi^-$, aiming at
the world-first detection of the X rays.
One is performed as a byproduct of J-PARC E07 experiment
(search for double hypernuclei with hybrid emulsion technique)
where $\Xi^-$ is stopped on the emulsion.
The other is a dedicated experiment for the detection of $\Xi^-$ Fe atom X rays (J-PARC E03).
The preliminary result of E07 and the status of the ongoing analysis for E03
are shown in this article.
Future prospects of $\Xi$-atomic X-ray spectroscopy are also discussed.