A disk brake apparatus that can suppress vibration and a brake noise phenomenon in a low deceleration range and increase braking force in a high deceleration range. In the low deceleration range a push surface at a tip of a small-diameter push portion of an inner piston pushes a back plate of a brake pad at a center of the push surface corresponding to a radial inside where deflection and inclination of a disk rotor is insignificant, thereby suppressing the vibration and brake noise phenomenon in the low deceleration range. In the high deceleration range the back plate of the brake pad is pushed at a radially outside push location of the disk rotor in an aperture-side end face of an outer piston, thereby making the braking force in the high deceleration range larger than the braking force in the low deceleration range.