A particle analyzing apparatus for analyzing a particle in a sample liquid, comprising a measuring chamber for containing the sample liquid containing the particle, a measuring flow path connected to the measuring chamber, a particle measuring device for outputting a measurement signal relating to the particle when it passes through the measuring flow path, a connecting conduit line with one end portion connected to an outlet end side of the measuring flow path, a first open-close mechanism provided on the connecting conduit line, a syringe device connected to the other end portion of the connecting conduit line, a second open-close mechanism connected to the syringe device and for releasing an inner space formed in a cylinder in the syringe device to the atmosphere, a pressure measuring part for measuring the pressure in the inner space, and a control device, wherein the control device comprises a first motion control part for closing the first open-close mechanism and opening the second open-close mechanism and for moving a piston of the syringe device to a predetermined advanced position L1, and then closing the second open-close mechanism and moving the piston to a predetermined backward position L2, thus forming an inner space S2 with a predetermined volume V2 and a negative pressure in the cylinder, a pressure value receiving part for receiving the measurement value of a pressure P2 in the inner space S2 with the negative pressure from the pressure measuring part, a second motion control part for opening the first open-close mechanism in a state where the inner space S2 with the negative pressure is formed, and sucking the sample liquid in the measuring chamber through the measuring flow path by the negative pressure to start particle measurement by the particle measuring device, a first calculating part for determining a particle analysis value A as a result of sucking at the pressure P2 based on the measurement signal obtained from the particle measuring device, and a second calculating part for performing calculation to correct the particle analysis value A based on the pressure P2 and a predetermined standard pressure Ps with respect to the inner space S2, wherein the standard pressure Ps is previously determined as a pressure produced in the cylinder by moving the piston from the predetermined forward position L1 to the predetermined backward position L2, wherein an atmospheric pressure is known at that time, the standard pressure Ps being retained or stored in the control device. a measuring chamber for containing the sample liquid containing the particle, a measuring flow path connected to the measuring chamber, a particle measuring device for outputting a measurement signal relating to the particle when it passes through the measuring flow path, a connecting conduit line with one end portion connected to an outlet end side of the measuring flow path, a first open-close mechanism provided on the connecting conduit line, a syringe device connected to the other end portion of the connecting conduit line, a second open-close mechanism connected to the syringe device and for releasing an inner space formed in a cylinder in the syringe device to the atmosphere, a pressure measuring part for measuring the pressure in the inner space, and a control device, wherein the control device comprises a first motion control part for closing the first open-close mechanism and opening the second open-close mechanism and for moving a piston of the syringe device to a predetermined advanced position L1, and then closing the second open-close mechanism and moving the piston to a predetermined backward position L2, thus forming an inner space S2 with a predetermined volume V2 and a negative pressure in the cylinder, a pressure value receiving part for receiving the measurement value of a pressure P2 in the inner space S2 with the negative pressure from the pressure measuring part, a second motion control part for opening the first open-close mechanism in a state where the inner space S2 with the negative pressure is formed, and sucking the sample liquid in the measuring chamber through the measuring flow path by the negative pressure to start particle measurement by the particle measuring device, a first calculating part for determining a particle analysis value A as a result of sucking at the pressure P2 based on the measurement signal obtained from the particle measuring device, and a second calculating part for performing calculation to correct the particle analysis value A based on the pressure P2 and a predetermined standard pressure Ps with respect to the inner space S2, wherein the standard pressure Ps is previously determined as a pressure produced in the cylinder by moving the piston from the predetermined forward position L1 to the predetermined backward position L2, wherein an atmospheric pressure is known at that time, the standard pressure Ps being retained or stored in the control device.