When a pipe pressure of a common discharge pipe during an independent discharge step in which only one reciprocating pump among a plurality of reciprocating pumps discharges a fluid to the common discharge pipe differs from internal pressures in pump chambers of the respective reciprocating pumps at discharge step start point angles, a stroke adjustment mechanism adjusts, on the basis of a pressure difference ΔP therebetween, effective stroke lengths of cross heads connected to plungers of the predetermined reciprocating pumps so that the internal pressures in the pump chambers reach the pipe pressure at the discharge step start point angles.