A fraudulent transmission data detection device (12, 14), comprising: a receiving unit that receives data that is transmitted in cycles; and a plurality of determination unit groups each comprising a plurality of determination units configured to operate in parallel with each other; wherein determination units belonging to different determination unit groups 46 take data items having mutually different IDs as their subjects for monitoring while determination units belonging to a same determination unit group take the same data items having a same ID as their subject for monitoring; and wherein the plurality of determination units within each determination unit group comprise: a first determination unit that, based on whether or not a time, from a first reference timing until a first predetermined number of data items are received by the receiving unit, is less than a first predetermined time, determines whether or not fraudulent transmission data is contained in the received data; and a second determination unit that, based on whether or not a time, from the first reference timing until a second predetermined number of data items, which is different from the first predetermined number of data items, are received by the receiving unit, is less than a second predetermined time that is different from the first predetermined time, determines whether or not fraudulent transmission data is contained in the received data; and/or a third determination unit that, based on whether or not a time, from a second reference timing, which is different from the first reference timing, of the first determination unit until the first predetermined number of data items are received by the receiving unit, is less than the first predetermined time, determines whether or not fraudulent transmission data is contained in the received data. a receiving unit that receives data that is transmitted in cycles; and a plurality of determination unit groups each comprising a plurality of determination units configured to operate in parallel with each other; wherein determination units belonging to different determination unit groups 46 take data items having mutually different IDs as their subjects for monitoring while determination units belonging to a same determination unit group take the same data items having a same ID as their subject for monitoring; and wherein the plurality of determination units within each determination unit group comprise: a first determination unit that, based on whether or not a time, from a first reference timing until a first predetermined number of data items are received by the receiving unit, is less than a first predetermined time, determines whether or not fraudulent transmission data is contained in the received data; and a second determination unit that, based on whether or not a time, from the first reference timing until a second predetermined number of data items, which is different from the first predetermined number of data items, are received by the receiving unit, is less than a second predetermined time that is different from the first predetermined time, determines whether or not fraudulent transmission data is contained in the received data; and/or a third determination unit that, based on whether or not a time, from a second reference timing, which is different from the first reference timing, of the first determination unit until the first predetermined number of data items are received by the receiving unit, is less than the first predetermined time, determines whether or not fraudulent transmission data is contained in the received data. a first determination unit that, based on whether or not a time, from a first reference timing until a first predetermined number of data items are received by the receiving unit, is less than a first predetermined time, determines whether or not fraudulent transmission data is contained in the received data; and a second determination unit that, based on whether or not a time, from the first reference timing until a second predetermined number of data items, which is different from the first predetermined number of data items, are received by the receiving unit, is less than a second predetermined time that is different from the first predetermined time, determines whether or not fraudulent transmission data is contained in the received data; and/or a third determination unit that, based on whether or not a time, from a second reference timing, which is different from the first reference timing, of the first determination unit until the first predetermined number of data items are received by the receiving unit, is less than the first predetermined time, determines whether or not fraudulent transmission data is contained in the received data.