| Summary: | We report the detection of the millimeter CH _3 OH masers including a new detection of class I (11 _0,11 –10 _1,10 A) and class II (6 _1,5 –5 _2,4 E) maser transitions toward the high-mass protostar S255IR NIRS3 in postburst phase. The CH _3 OH emissions were detected as a mixture of maser and thermal characteristics. We examine the detected transitions using an excitation diagram and local thermodynamic equilibrium model spectra and compare the observed properties with those of thermal lines. Class II CH _3 OH maser transitions showed distinctive intensity and velocity distributions from those of thermal transitions. Bright, distinct emission components in addition to the fragmented and arc-shaped emissions are only detected in class I CH _3 OH maser transitions toward southern and western directions from the protostellar position, implying the presence of the slow outflow shocks.
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