Provided is a device for testing solubility of drugs in gastrointestinal tract. The device for testing solubility includes: a plurality of vessels respectively corresponding to gastrointestinal tract of a living body; digestive juice supply devices supplying digestive juice to the vessel requiring the supply of the digestive juice; liquid delivery paths each being provided between the vessels and extending from an upstream-side vessel to a downstream-side vessel; delivery driving sources applying a fluid force to a mixed liquid of the digestive juice and an oral drug in the liquid delivery paths; and a control device controlling delivery speeds of the delivery driving sources according to a temporal change of a flow rate from an upstream side to a downstream side of the gastrointestinal tract of the living body.