An operation monitoring device comprising: a performance information collection means for collecting a plurality of types of performance information of an operation monitoring target machine; a performance analysis means for analyzing said performance information collected by said performance information collection means; a performance information grouping means for generating a group that includes a plurality of types of said performance information of said operation monitoring target machine based on a predetermined condition; and a monitoring condition alteration means for making said performance information collection means perform collection of a representative type of said performance information for said group generated by said performance information grouping means at a predetermined interval, said monitoring condition alteration means being adapted for - making said performance information collection means stop collection of a non-representative type of said performance information for said group, said non-representative type being other type than said representative type of said performance information for said group, or - making said performance information collection means perform collection thereof at a first interval which is longer than the interval for said representative type of said performance information, and wherein, in case that a fluctuation rate or a fluctuation amount of said representative type of said performance information exceeds a predetermined threshold value, the monitoring condition alteration means being further adapted for - making said performance information collection means start collection of said non-representative type of said performance information or - making said performance information collection means perform collection thereof at a second interval which is shorter than said first interval. a performance information collection means for collecting a plurality of types of performance information of an operation monitoring target machine; a performance analysis means for analyzing said performance information collected by said performance information collection means; a performance information grouping means for generating a group that includes a plurality of types of said performance information of said operation monitoring target machine based on a predetermined condition; and a monitoring condition alteration means for making said performance information collection means perform collection of a representative type of said performance information for said group generated by said performance information grouping means at a predetermined interval, said monitoring condition alteration means being adapted for - making said performance information collection means stop collection of a non-representative type of said performance information for said group, said non-representative type being other type than said representative type of said performance information for said group, or - making said performance information collection means perform collection thereof at a first interval which is longer than the interval for said representative type of said performance information, and wherein, in case that a fluctuation rate or a fluctuation amount of said representative type of said performance information exceeds a predetermined threshold value, the monitoring condition alteration means being further adapted for - making said performance information collection means start collection of said non-representative type of said performance information or - making said performance information collection means perform collection thereof at a second interval which is shorter than said first interval. - making said performance information collection means stop collection of a non-representative type of said performance information for said group, said non-representative type being other type than said representative type of said performance information for said group, or - making said performance information collection means perform collection thereof at a first interval which is longer than the interval for said representative type of said performance information, - making said performance information collection means start collection of said non-representative type of said performance information or - making said performance information collection means perform collection thereof at a second interval which is shorter than said first interval.