The reference interaction site model self-consistent-field (RISM-SCF) method is applied to study the solvent effect on the keto-enol tautomers of formamide in aprotic solvents. Six aprotic solvents-carbon tetrachloride (CCl4), carbon disulfide (CS2), dimethyl ether (DME), tetrahydrofuran (THF), acetonitrile (CH3CN), and dimethyl sulfoxide (DMSO)-are examined. We present detailed analyses of the solvent effects on solvation free energies, solvation structures, and solute electronic structures from a microscopic point of view. Good correlation between the calculated depth of the first minimum in the first solvation shell and the empirical solvent parameters representing solute-solvent hydrogen bonding is found, which provides a microscopic interpretation of the parameters. The solvation free energy does not increase monotonically with an increase of solvent polarity, and a remarkable irregularity is seen for acetonitrile.