NEW MATERIAL:A butyric acid derivative expressed by formula I, lower alkyl ester thereof, butyric acid derivative expressed by formula II (R is lower alkyl; X is halogen), azepinobenzimidazole derivative expressed by formula III and pharmacologically acceptable salt thereof.

EXAMPLE: 1,2,3,4-Tetrahydro-6-methyl-4-oxo-azepino[1,2-a]benzimidazole hydrochlo ride.

USE: An antipyretic agent, tranquilizer or raw material therefor.

PREPARATION: (i) The 2-position of benzimidazole is substituted by CH3 group and (ii) the nitrogen atom at the 1-position is substituted by a butyric acid ester to afford the compound expressed by formula I. (iii) The resultant ester is then set free and (iv) a halogenoalkylating agent is reacted to protect the nitrogen atom at the 3-position and provide the compound expressed by formula II. (iv) A condensing agent is then reacted therewith to prepare the compound expressed by formula III.