PURPOSE: To obtain the title fluid having a high electroviscous effect and a low base viscosity by mixing a liquid crystal compound derived by bonding liquid crystal groups to a flexible molecular chain with a side chain type liquid crystal compound having a specified liquid crystal bonding ratio.

CONSTITUTION: The title fluid comprises a liquid crystal compound derived by bonding a plurality of liquid crystal groups to a flexible molecular chain and at least one side chain type liquid crystal compound of a liquid crystal bonding ratio of 30% or below (1: liquid crystal group; 2: flexible molecular chain, 3: flexible molecular chain optionally added; and 4: spacer). The amount of the side chain type liquid crystal compound used is desirably 20-80% more desirably 30-70%. This fluid can be stably used for a long time in a new compact electronically controlled and operated actuator for e.g. a valve, a clutch, a brake or a torque converter.