To provide an admixture for improving the workability of an inorganic binder composition, and a phenolic resin-based dispersant.SOLUTION: An admixture for improving the workability of an inorganic binder composition according to the present invention contains or consists of: 20-80 mass% of at least one dispersant; 10-45 mass% of at least one polycarboxylic acid polymer; 1-20 mass% of a retarder; and optionally, a further additive, with the balance being water up to 100 mass%. The dispersant is a phenolic resin-based dispersant resulting from a specific polycondensation reaction.SELECTED DRAWING: None