Apparatus and method for estimating flow velocity of fluid

An apparatus includes a solenoid valve and a pressure sensor disposed in a water pipe in this order from an upstream end, and a control unit controlling open/close of the solenoid valve and receives a sensor signal outputted from the pressure sensor. The controller obtains a difference between a water pressure measured by the pressure sensor when it is determined that the decreased degree of opening is increased, and a water pressure measured by the pressure sensor when a flow velocity is zero, and calculates a loss coefficient of an upstream water pipe located upstream from the solenoid valve based on the pressure difference and a flow velocity calculated based on a loss coefficient of the solenoid valve. The controller estimates a flow velocity of the water currently flowing in the water pipe based on the loss coefficient and the difference between water pressures of the last and present measurements.