Abstract: A differential pressure detection equipment typically represented by a water level measuring apparatus provided for a nuclear power plant includes a condenser having a steam flow-in port connected to a steam phase side pressure detector through a connection pipe, a reference water column side instrument pipe connected to a bottom portion of the condenser, a variable water column side instrument pipe connected to a liquid phase side pressure detector and a pressure difference detector connected to both the instrument pipes for detecting a pressure difference between a reference water head pressure of the reference water column side instrument pipe and a variable water head pressure of the variable water column side instrument pipe. The connection pipe has an upward inclination .theta. from the steam phase side pressure detector to the condenser so as to satisfy an equation of 0<tan .theta.<D/L, in which D is an inner diameter of the connection pipe and L is an axial length of the connection pipe.