  We show that a quantum scar state, an atypical eigenstate breaking eigenstate
thermalization hypothesis embedded in a many-body energy spectrum, can be
constructed in flat band systems. The key idea of our construction is to make
use of orthogonal compact localized states. We concretely discuss our
construction scheme, taking a saw-tooth flat lattice system as an example, and
numerically demonstrate the presence of a quantum scar state. Examples of
higher-dimensional systems are also addressed. Our construction method of
quantum scar has broad applications to various flat band systems.
