  We investigate what kind of Markovian quantum master equation (QME) in the
Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) form is realized under
Poincar\'{e} symmetry. The solution of the Markovian QME is given by a quantum
dynamical semigroup, for which we introduce invariance under Poincar\'{e}
transformations. Using the invariance of the dynamical semigroup and applying
the unitary representation of Poincar\'{e} group, we derive the Markovian QME
for a relativistic massive spin-0 particle. Introducing the field operator of
the massive particle and examining its evolution, we find that the field
follows a dissipative Klein-Gordon equation. In addition, we show that any two
local operators for spacelike separated regions commute with each other. This
means that the microcausality condition is satisfied for the dissipative model
of the massive particle.
