Novel azine derivative compounds represented by the following general formula (I), which are stably and highly effective against a wide spectrum of plant diseases even when used in a low concentration; a process for producing these; and a bactericide especially for agricultural or horticultural use which contains any of these compounds as an active ingredient. (I) In the formula (I), R1 represents hydrogen, alkyl, alkenyl, alkynyl, acyl, alkoxyalkyl, alkoxycarbonylalkyl, or haloalkyl; R2 represents alkyl, alkenyl, alkynyl, alkoxyalkyl, haloalkyl, or cycloalkylalkyl; R3 and R4 each represents hydrogen or alkyl; Hetero represents a fused ring containing heteroatoms; and X represents hydrogen, alkyl, or alkoxy.