A brake apparatus applied to a vehicle comprising a regenerative braking device configured to generate regenerative braking force by converting a kinetic energy of a rotating wheel into an electrical energy and collecting the electrical energy to a battery, comprising: a master cylinder configured to output a hydraulic pressure of a hydraulic fluid according to a brake operation by a driver, a wheel cylinder which is disposed for each wheel and configured to operate a friction member with the hydraulic pressure of the hydraulic fluid to generate friction braking force, a first actuator which is disposed in a passage of the hydraulic fluid between said master cylinder and said wheel cylinder and configured to adjust the hydraulic pressure supplied to said wheel cylinder, and a first electronic control unit which is configured to set up target hydraulic pressure so that the sum of said regenerative braking force and said friction braking force becomes equal to target total braking force set up according to the amount of a brake operation, and to control an operation of said first actuator so that the outputted hydraulic pressure of said first actuator follows said target hydraulic pressure, characterized by a second actuator which is disposed in a passage of the hydraulic fluid between said first actuator and said wheel cylinder, configured to supply the hydraulic pressure outputted from said first actuator to said wheel cylinder as it is when being not in operation, and configured to individually adjust the hydraulic pressure of each wheel cylinder when being in operation, a second electronic control unit which is configured to control an operation of said second actuator to carry out an antilock control for suppressing the lock of a wheel at least, and a communication connection means to connect said first electronic control unit and said second electronic control unit so that they can communicate each other, wherein said first electronic control unit is configured to change the control mode into a control mode on the assumption that said second actuator is operating, when said first electronic control unit receives operation information which shows that said second actuator is operating and is transmitted from said second electronic control unit, wherein: said first electronic control unit comprises an operation start estimation means (S61-S69) which is configured to judge whether a variation of the hydraulic pressure with respect to the flow rate of the hydraulic fluid outputted from said first actuator is larger than an assumed maximum value of the variation of the hydraulic pressure with respect to the flow rate of the hydraulic fluid outputted from said first actuator in a status that said first actuator and said wheel cylinder are communicating with each other and, based on the judgment result, to estimate whether the operation of said second actuator has been started, and said first electronic control unit comprises an early control mode changing means (S17, S30) for changing the control mode into said control mode on the assumption that said second actuator is operating, without waiting for the reception of said operation information, when said operation start estimation means (S61-S69) estimates that the operation of said second actuator has been started. a master cylinder configured to output a hydraulic pressure of a hydraulic fluid according to a brake operation by a driver, a wheel cylinder which is disposed for each wheel and configured to operate a friction member with the hydraulic pressure of the hydraulic fluid to generate friction braking force, a first actuator which is disposed in a passage of the hydraulic fluid between said master cylinder and said wheel cylinder and configured to adjust the hydraulic pressure supplied to said wheel cylinder, and a first electronic control unit which is configured to set up target hydraulic pressure so that the sum of said regenerative braking force and said friction braking force becomes equal to target total braking force set up according to the amount of a brake operation, and to control an operation of said first actuator so that the outputted hydraulic pressure of said first actuator follows said target hydraulic pressure, said first electronic control unit comprises an operation start estimation means (S61-S69) which is configured to judge whether a variation of the hydraulic pressure with respect to the flow rate of the hydraulic fluid outputted from said first actuator is larger than an assumed maximum value of the variation of the hydraulic pressure with respect to the flow rate of the hydraulic fluid outputted from said first actuator in a status that said first actuator and said wheel cylinder are communicating with each other and, based on the judgment result, to estimate whether the operation of said second actuator has been started, and said first electronic control unit comprises an early control mode changing means (S17, S30) for changing the control mode into said control mode on the assumption that said second actuator is operating, without waiting for the reception of said operation information, when said operation start estimation means (S61-S69) estimates that the operation of said second actuator has been started.