PURPOSE: To prevent sedimentation of particles or the like in a high-viscosity liquid, by providing a two-port ball valve for relief in parallel with a four-port ball valve for picking up the high-viscosity liquid and flowing always the high- viscosity liquid in a certain speed in a circulating line.

CONSTITUTION: At the normal time when sampling is not performed, a ball valve 10B of a four-port ball valve 10 forms a horizontal flow passage, and a two- port ball valve 11 provided in parallel with the four-port ball valve 10 in a by- pass line 9 cuts off the by-pass line 9. In case of sampling, the ball valve 10B of the four-port ball valve 10 for picking up the high-viscosity liquid forms a vertical flow passage, and simultaneously, high-pressure air is sent from an air head 17 to the vertical flow passage formed by turning of the ball valve 10B, and the high-viscosity liquid 2 picked up to the flow passage of the ball valve 10B is extruded into a sample vessel 16 through a picking-up tube 14.