A measuring and assessing method for the AC corrosion risk of a pipeline, wherein the coupon is connected to a metallic pipeline buried in the earth and the AC corrosion risk of the pipeline is assessed on the basis of coupon DC current density and coupon AC current density that are acquired from a measured value of a coupon current, wherein the measuring and assessing method comprises: a step of specifying frequency by means of a control device to specify a frequency of a source of AC corrosion from a waveform of the measured value of the coupon current; prior to a step of calculating coupon current density whereby a pair of coupon DC current density and coupon AC current density is acquired from a measured value of a coupon current in one time unit by defining one cycle of the specified frequency as one time unit, and a step of assessing the AC corrosion risk by means of said pair of coupon DC current density and coupon AC current density which are acquired by said step of calculating coupon current density, and said step of specifying frequency includes: sequentially selecting a frequency from among commercial frequencies of 16-2/3Hz, 50Hz and 60Hz; extracting a waveform of a measured value of a coupon current with one cycle of the selected frequency; judging whether or not a difference in appearance time between a maximum value and a minimum value in an extracted waveform is equal to 1/2 of one cycle of the selected frequency; and specifying the selected frequency as the frequency of the source of AC corrosion when a result of the judging matches, and said step of assessing the AC corrosion risk includes: comparing values of said pair of coupon DC current density and coupon AC current density acquired by said step of calculating coupon current density with a cathodic protection reference which employs the coupon current density as an index. a step of specifying frequency by means of a control device to specify a frequency of a source of AC corrosion from a waveform of the measured value of the coupon current; prior to a step of calculating coupon current density whereby a pair of coupon DC current density and coupon AC current density is acquired from a measured value of a coupon current in one time unit by defining one cycle of the specified frequency as one time unit, and a step of assessing the AC corrosion risk by means of said pair of coupon DC current density and coupon AC current density which are acquired by said step of calculating coupon current density, and said step of specifying frequency includes: sequentially selecting a frequency from among commercial frequencies of 16-2/3Hz, 50Hz and 60Hz; extracting a waveform of a measured value of a coupon current with one cycle of the selected frequency; judging whether or not a difference in appearance time between a maximum value and a minimum value in an extracted waveform is equal to 1/2 of one cycle of the selected frequency; and specifying the selected frequency as the frequency of the source of AC corrosion when a result of the judging matches, and sequentially selecting a frequency from among commercial frequencies of 16-2/3Hz, 50Hz and 60Hz; extracting a waveform of a measured value of a coupon current with one cycle of the selected frequency; judging whether or not a difference in appearance time between a maximum value and a minimum value in an extracted waveform is equal to 1/2 of one cycle of the selected frequency; and specifying the selected frequency as the frequency of the source of AC corrosion when a result of the judging matches, and said step of assessing the AC corrosion risk includes: comparing values of said pair of coupon DC current density and coupon AC current density acquired by said step of calculating coupon current density with a cathodic protection reference which employs the coupon current density as an index. comparing values of said pair of coupon DC current density and coupon AC current density acquired by said step of calculating coupon current density with a cathodic protection reference which employs the coupon current density as an index.