According to an embodiment of an autosampler, a sample rack provided with a thermal conductive plate holder on whose upper surface a sample plate is to be set is set on a rack setting section. A cooling device for cooling the plate holder is provided. A plate detection section for detecting whether a sample plate is set on the plate holder of the sample rack that is set on the rack setting section is provided, and when a sample plate is not set on the plate holder of the sample rack that is set on the rack setting section, the output of the cooling device for cooling the plate holder is turned off.