A cylinder apparatus for a brake may include: a piston configured to reciprocate in a cylinder body; a rod coaxially coupled to the piston; a stopper disposed in the cylinder body with the rod penetrated and inserted into the stopper; and an elastic member disposed between the piston and the stopper and configured to elastically support the piston in a direction away from the stopper. The piston and the rod may be integrally formed by injection molding.