Provided is a mononuclear ruthenium complex that comprises a ruthenium-silicon bond that is represented by formula (1) and that exhibits excellent catalyst activity in each of a hydrosilylation reaction, a hydrogenation reaction, and reduction of a carbonyl compound. In formula (1), R1-R6 either independently represent an alkyl group, an aryl group, an aralkyl group or the like that may be substituted with a hydrogen atom or X, or represent a crosslinking substituent in which at least one pair comprising one of R1-R3 and one of R4-R6 is combined. X represents a halogen atom, an organoxy group, or the like. L represents a two-electron ligand other than CO and phosphine. When a plurality of L are present, the plurality of L may be the same as or different from each other. When two L are present, the two L may be bonded to each other. n and m independently represent an integer of 1 to 3 with the stipulation that n + m equals 3 or 4.