A fraud detection system comprising a server, a user terminal, a facility terminal, and a detection device for executing predetermined processing when a detection target is detected by using the detection device connected to the facility terminal, the user terminal comprising action determination means configured to determine, before the detection target is detected, whether a predetermined action has been performed by a user having the user terminal; the server comprising fraud detection means configured to execute, when it is determined that the predetermined action has been performed and before the detection target is detected, fraud detection on the user based on identification information stored in the user terminal; and the facility terminal comprising execution means configured to execute, when the detection target is detected, the predetermined processing based on an execution result of the fraud detection, wherein the detection target is a code displayed on the user terminal, wherein the detection device is used to detect the code, and is external to the user terminal, wherein the predetermined action is a display action for displaying the code on the user terminal, wherein the action determination means is configured to determine, before the code is detected, whether the display action has been performed, wherein, when it is determined that the display action has been performed, the fraud detection means is configured to execute the fraud detection based on the identification information, and wherein, when the code is detected, the execution means is configured to execute the predetermined processing based on the execution result of the fraud detection, the server further comprising: calculation means configured to calculate, by using a learning model for probability calculation, a probability that the code displayed on the user terminal is to be used by the user, wherein, when it is determined that the display action has been performed, the fraud detection means is configured not to execute the fraud detection when the calculated probability corresponding to the user is less than a threshold. the user terminal comprising action determination means configured to determine, before the detection target is detected, whether a predetermined action has been performed by a user having the user terminal; the server comprising fraud detection means configured to execute, when it is determined that the predetermined action has been performed and before the detection target is detected, fraud detection on the user based on identification information stored in the user terminal; and the facility terminal comprising execution means configured to execute, when the detection target is detected, the predetermined processing based on an execution result of the fraud detection, wherein the detection target is a code displayed on the user terminal, wherein the detection device is used to detect the code, and is external to the user terminal, wherein the predetermined action is a display action for displaying the code on the user terminal, wherein the action determination means is configured to determine, before the code is detected, whether the display action has been performed, wherein, when it is determined that the display action has been performed, the fraud detection means is configured to execute the fraud detection based on the identification information, and wherein, when the code is detected, the execution means is configured to execute the predetermined processing based on the execution result of the fraud detection, the server further comprising: calculation means configured to calculate, by using a learning model for probability calculation, a probability that the code displayed on the user terminal is to be used by the user, wherein, when it is determined that the display action has been performed, the fraud detection means is configured not to execute the fraud detection when the calculated probability corresponding to the user is less than a threshold. calculation means configured to calculate, by using a learning model for probability calculation, a probability that the code displayed on the user terminal is to be used by the user, wherein, when it is determined that the display action has been performed, the fraud detection means is configured not to execute the fraud detection when the calculated probability corresponding to the user is less than a threshold.