This fraudulent message detection device for detecting a fraudulent message sent to a bus is provided with: a resynchronization detection unit (124) that, for the purpose of adjusting a sampling point to acquire a logical value of a signal on a bus during a one-bit period, determines whether or not to execute resynchronization by detecting a deviation from an edge of the signal; a transmission/reception control unit (122) that, during a one-bit period following the detection of the edge by the resynchronization detection unit (124), acquires a first logical value, which is the logical value on the bus at the sampling point being used prior to the detection, and a second logical value, which is the logical value on the bus at a post-resynchronization sampling point based on the edge; a comparison unit (627) that compares the first and second logical values; and a fraud detection process unit (628) that executes a fraud-detection-instance process when the first logical value and the second logical value do not
