In addition to PM total matter, PM size distribution is recently receiving increased attention because of the dependency of PM size on human health effects. Thus, PM size distributions and the emission behavior under various driving patterns are becoming important in diesel particulate emissions.Electrical Low Pressure Impactor (ELPI)_is a candidate to measure continuously, not only PM mass, but also particulate size distribution. Therefore, we investigated using ELPI to measure diesel particulate mass and size distribution, together with time series behaviors under various driving patterns.This study demonstrated the feasibility of continuous measurement of PM size distribution by means of an ELPI. The typical PM size distribution curve on weight base has a peak of 0.18 micrometer. The typical PM size distribution curve on number base has a peak of 0.11 micrometer. Engine load influences these characteristics. These characteristics showed similar tendencies on both a constant speed test and a transient speed test.