A solid-phase extraction apparatus comprising: a pressurizing syringe pump arranged to carry out operations of suction and discharge of air; an air feed pipe arranged to feed the air; an air-feed-pipe pressure sensor arranged to monitor a pressure in the air feed pipe; a solid-phase extraction cartridge provided with a solid-phase extraction material; a sample dispensing nozzle arranged to suction and discharge a sample solution; a sample-dispensing syringe pump arranged to carry out operations of suction and discharge of the sample solution; a solution feed pipe arranged to connect the sample dispensing nozzle and the sample-dispensing syringe pump; and a control unit arranged to carry out a solid-phase extraction process of operating the sample-dispensing syringe pump, suctioning the sample solution from the sample dispensing nozzle, discharging the sample solution to the solid-phase extraction cartridge, operating the pressurizing syringe pump, feeding the air to the solid-phase extraction cartridge to apply pressure to the sample solution in the solid-phase extraction cartridge, and extracting a measurement component from the sample solution, wherein the pressurising syringe pump is arranged to apply a pressure to the sample solution to make the measurement component in the sample solution adsorbed on the solid-phase extraction material, to apply pressure to cleaning solution to make impurities other than the measurement component cleaned from the solid-phase extraction material after the absorption, and to apply a pressure to an eluting solution to make the measurement component eluted from the solid-phase extraction material after the cleaning, characterised by: a solution-feed-pipe pressure sensor arranged to measure a pressure in the solution feed pipe; and wherein the control unit has a converting unit arranged to obtain viscosity information of the sample solution based on the pressure measured by the solution-feed-pipe pressure sensor and to determine the pressure to be applied by the pressurizing syringe pump to the solid-phase extraction cartridge based on the viscosity information of the sample solution, to obtain an optimum collection rate; and when a plurality of measurement components are extracted at the same time, the converting unit is arranged to determine the pressure that decreases the difference between the collection rates of the plurality of measurement components. a pressurizing syringe pump arranged to carry out operations of suction and discharge of air; an air feed pipe arranged to feed the air; an air-feed-pipe pressure sensor arranged to monitor a pressure in the air feed pipe; a solid-phase extraction cartridge provided with a solid-phase extraction material; a sample dispensing nozzle arranged to suction and discharge a sample solution; a sample-dispensing syringe pump arranged to carry out operations of suction and discharge of the sample solution; a solution feed pipe arranged to connect the sample dispensing nozzle and the sample-dispensing syringe pump; and a control unit arranged to carry out a solid-phase extraction process of operating the sample-dispensing syringe pump, suctioning the sample solution from the sample dispensing nozzle, discharging the sample solution to the solid-phase extraction cartridge, operating the pressurizing syringe pump, feeding the air to the solid-phase extraction cartridge to apply pressure to the sample solution in the solid-phase extraction cartridge, and extracting a measurement component from the sample solution, wherein the pressurising syringe pump is arranged to apply a pressure to the sample solution to make the measurement component in the sample solution adsorbed on the solid-phase extraction material, to apply pressure to cleaning solution to make impurities other than the measurement component cleaned from the solid-phase extraction material after the absorption, and to apply a pressure to an eluting solution to make the measurement component eluted from the solid-phase extraction material after the cleaning, characterised by: a solution-feed-pipe pressure sensor arranged to measure a pressure in the solution feed pipe; and wherein the control unit has a converting unit arranged to obtain viscosity information of the sample solution based on the pressure measured by the solution-feed-pipe pressure sensor and to determine the pressure to be applied by the pressurizing syringe pump to the solid-phase extraction cartridge based on the viscosity information of the sample solution, to obtain an optimum collection rate; and when a plurality of measurement components are extracted at the same time, the converting unit is arranged to determine the pressure that decreases the difference between the collection rates of the plurality of measurement components. a solution-feed-pipe pressure sensor arranged to measure a pressure in the solution feed pipe; and wherein the control unit has a converting unit arranged to obtain viscosity information of the sample solution based on the pressure measured by the solution-feed-pipe pressure sensor and to determine the pressure to be applied by the pressurizing syringe pump to the solid-phase extraction cartridge based on the viscosity information of the sample solution, to obtain an optimum collection rate; and when a plurality of measurement components are extracted at the same time, the converting unit is arranged to determine the pressure that decreases the difference between the collection rates of the plurality of measurement components.