A motion prediction method, performed by a motion prediction apparatus, of computing a lane change probability indicating a probability of a second vehicle conducting a lane change in front of the own vehicle from an adjacent lane into an own lane in which the own vehicle is running, according to a state quantity corresponding to a behavior of the second vehicle running in the adjacent lane to the own lane, and predicting the lane change to be conducted by the second vehicle with use of the lane change probability and a preset threshold value, comprising the step of computing the lane change probability with no use of a lane width (32a, 32b) of the adjacent lane according to the state quantity; characterized by the steps of: obtaining information indicating the lane width (32a, 32b) of the adjacent lane; correcting, according to the lane width (32a, 32b), at least one of the computed lane change probability and the preset threshold value; and comparing the corrected lane change probability with the preset threshold value, or comparing the computed lane change probability with the corrected threshold value, or comparing the corrected lane change probability with the corrected threshold value, thereby predicting whether or not the second vehicle conducts the lane change, wherein the correcting, according to the lane width (32a, 32b), of the lane change probability is to change, according to the lane width (32a, 32b), a weight applied to the state quantity; wherein the correcting, according to the lane width (32a, 32b), of the preset threshold value includes: selecting, from among different threshold values set beforehand for the lane widths of the adjacent lane, a threshold value corresponding to the lane width indicated by the obtained information. computing the lane change probability with no use of a lane width (32a, 32b) of the adjacent lane according to the state quantity; characterized by the steps of: obtaining information indicating the lane width (32a, 32b) of the adjacent lane; correcting, according to the lane width (32a, 32b), at least one of the computed lane change probability and the preset threshold value; and comparing the corrected lane change probability with the preset threshold value, or comparing the computed lane change probability with the corrected threshold value, or comparing the corrected lane change probability with the corrected threshold value, thereby predicting whether or not the second vehicle conducts the lane change, wherein the correcting, according to the lane width (32a, 32b), of the lane change probability is to change, according to the lane width (32a, 32b), a weight applied to the state quantity; wherein the correcting, according to the lane width (32a, 32b), of the preset threshold value includes: selecting, from among different threshold values set beforehand for the lane widths of the adjacent lane, a threshold value corresponding to the lane width indicated by the obtained information. obtaining information indicating the lane width (32a, 32b) of the adjacent lane; correcting, according to the lane width (32a, 32b), at least one of the computed lane change probability and the preset threshold value; and comparing the corrected lane change probability with the preset threshold value, or comparing the computed lane change probability with the corrected threshold value, or comparing the corrected lane change probability with the corrected threshold value, thereby predicting whether or not the second vehicle conducts the lane change, wherein the correcting, according to the lane width (32a, 32b), of the lane change probability is to change, according to the lane width (32a, 32b), a weight applied to the state quantity; wherein the correcting, according to the lane width (32a, 32b), of the preset threshold value includes: selecting, from among different threshold values set beforehand for the lane widths of the adjacent lane, a threshold value corresponding to the lane width indicated by the obtained information.