Provided is a fraudulent message detection device that detects a fraudulent message in a bus network and includes: a resynchronization detector that detects an edge of a signal on a bus in the bus network and determines whether to perform resynchronization, so as to adjust a sampling point in a one-bit period; a transmission and receiving control unit that obtains a first logical value and a second logical value in a one-bit period after the resynchronization detector determines to perform the resynchronization, the first logical value being a logical value at a sampling point used before the edge is detected, the second logical value being a logical value at a sampling point after the resynchronization is performed; a comparator that compares the first and second logical values; and a fraud detection processing unit that executes post-fraud-detection processing, when the first and second logical values do not coincide.