A fluid agitation method is provided, whereby a swirling flow is generated in a trace amount of fluid, thereby agitating the fluid. The fluid agitation method includes introducing the fluid into an agitation chamber (3) including a wall having an uneven mass distribution, and applying oscillation (F) to the wall with frequencies varying in a predetermined frequency range. The uneven mass distribution of the wall is attained, for example, by arranging a plurality of thickened portions (11 to 18) of different thicknesses in a ring.