A data processing device for detecting the abnormal operation of a CPU is provided. The data processing device comprises a CPU, an interrupt counter, and a counter-abnormal-value detection circuit. The interrupt counter increments a count value based on an interrupt start signal which is outputted in response to an interrupt signal indicative of an interrupt request to the CPU and which indicates that the interrupt request has been accepted, and decrements the count value based on an end-of-interrupt signal which indicates that processing corresponding to the interrupt has completed. The counter-abnormal-value detection circuit detects abnormalities by comparing the count value with a predetermined value.