  In the interstellar medium (ISM), the complex organic molecules that contain
the thiol group ($-$SH) play an important role in the polymerization of amino
acids. We look for SH-bearing molecules in the chemically rich solar-type
protostar IRAS 16293-2422. After the extensive spectral analysis using the
local thermodynamic equilibrium (LTE) model, we have detected the rotational
emission lines of trans-isomer monothioformic acid (t-HC(O)SH) towards the IRAS
16293 B using the Atacama Large Millimeter/Submillimeter Array (ALMA). We did
not observe any evidence of cis-isomer monothioformic acid (c-HC(O)SH) towards
the IRAS 16293 B. The column density of t-HC(O)SH towards the IRAS 16293 B was
(1.02$\pm$0.6)$\times$10$^{15}$ cm$^{-2}$ with an excitation temperature of
125$\pm$15 K. The fractional abundance of t-HC(O)SH with respect to H$_{2}$
towards the IRAS 16293 B is 8.50$\times$10$^{-11}$. The column density ratio of
t-HC(O)SH/CH$_{3}$SH towards the IRAS 16293 B is 0.185. We compare our
estimated abundance of t-HC(O)SH towards the IRAS 16293 B with the abundance of
t-HC(O)SH towards the galactic center quiescent cloud G+0.693-0.027 and hot
molecular core G31.41+0.31. After the comparison, we found that the abundance
of t-HC(O)SH towards the IRAS 16293 B is several times of magnitude lower than
G+0.693-0.027 and G31.41+0.31. We also discuss the possible formation mechanism
of t-HC(O)SH in the ISM.
