Provided is a liquid reagent containing microchip having a fluid circuit formed of a space inside thereof. Liquid present in the fluid circuit is transferred to a desired position in the fluid circuit by applying centrifugal force. The fluid circuit includes a reagent retaining portion for accommodating a liquid reagent. The microchip includes an air introduction path formed of a groove provided on an outer surface of the microchip and coupled to the reagent retaining portion for introducing air into the reagent retaining portion, and a sealing portion provided so as to be detachable from the microchip for sealing the air introduction path. A method of using the microchip and a packaged liquid reagent containing microchip using the microchip are also provided.