A brake apparatus improved in mountability on a vehicle is provided. The apparatus includes a master cylinder 4 that generates hydraulic brake pressure by a driver's brake operation, and a stroke simulator 5 that creates an artificial operation reaction force of a brake operation member when the brake fluid flown out of the master cylinder 4 enters the stroke simulator 5. The master cylinder 4 and the stroke simulator 5 are integrally arranged to overlap each other in a perpendicular direction (as viewed from the perpendicular direction) when installed in the vehicle.