Ventilating fan for building

A ventilation fan for a building is provided to control power supplied to a fan driving motor in accordance with an exhaust load of the ventilation fan to maintain a pleasant state of an indoor space while preventing waste of power and extending the life span of the ventilation fan. A control unit controls power supplied to a motor(105) in accordance with a signal value inputted through a rotation sensor to increase or decrease rpm of the motor. The control unit includes a micro controller unit, a motor voltage control unit controlling a voltage outputted to the motor in accordance with rpm of a fan detected by the rotation sensor, a motor input and output unit inputting the signal received from the rotation sensor to the micro controller unit and outputting the controlled voltage to the motor, and a power part supplying an operation voltage of the motor and other circuit parts.