The present invention relates to a water supply of the coffee making apparatus alarm, the microprocessor 50 that controls the overall operation of the coffee maker and; A key signal having a driving key, and in that the drive key and the key input unit 51 to be applied to the microcomputer 50; Having a plurality of keys to display the number of people and the selected water level setting unit 52 for applying a water level set signal corresponding to the number of people in the microcomputer 50, and; By having a float which moves up / down in a water bath with the amount of water supplied to the water tank 530, a float sensor (53) for applying a variable voltage signal (Vo) according to the movement of the float in the microcomputer 50 and the .; Including; lamp 562 and drives the buzzer 563, the water level alarm unit 56 indicating that the water in the tank as the water level set by the level setting section 52 according to a control signal output from the microcomputer 50 do. The invention by the installation, and water as much as the selected person by a user when the alarm it achieved a float sensor to detect the water supply to the water tank 530 in the water tank provided in the coffee maker, the exact desired amount of water supply can do.