An autosampler is switched selectively between an injecting mode where a sampling flow path is incorporated into an analysis flow path of a liquid chromatograph and a loading mode where the sampling flow path is not incorporated into the analysis flow path and injects a sample into the analysis flow path at a position farther upstream than a separation column by being switched to the injecting mode with the sample held in the sampling flow path, and includes a clog determiner configured to acquire a sending liquid pressure of a liquid sending pump that sends a mobile phase in the analysis flow path, obtain a variation value of the liquid sending pressure when the injecting mode and the loading mode are switched and determine presence or absence of a clog in a system incorporated into the analysis flow path in the injecting mode based on the obtained variation value.