A driver condition determination device that is configured to determine whether a driver of a vehicle has degraded consciousness, comprising: a proximity condition calculating section that is configured to calculate a proximity to a preceding vehicle positioned in front of the vehicle; an operation condition detecting section that is configured to detect an accelerating operation condition of the driver; a distribution generating section that is configured to generate a distribution of the accelerating operation condition of the driver with respect to the proximity, wherein the distribution indicates a relationship between proximities calculated by the proximity condition calculating section and accelerating operation conditions detected by the operation condition detecting section based on data sampling repeatedly performed over a predetermined time; a likelihood calculating section that is configured to calculate a likelihood, said likelihood indicating a likelihood of the accelerating operation condition of the driver detected by the operation condition detecting section with respect to the proximity calculated by the proximity condition calculating section, and a likelihood threshold value from the distribution generated by the distribution generating section; and a degraded consciousness determining section that is configured to determine whether the driver has the degraded consciousness, wherein the proximity condition calculating section is configured to calculate, as the proximity, an index of perceptual risk estimate, PRE, by the expression PRE=(Vr+α·Vs+β·Ax)/D n, where Vr represents the relative speed of the vehicle with respect to the preceding vehicle, Vs represents the vehicle speed of the vehicle, Ax represents the relative acceleration of the vehicle with respect to the preceding vehicle, D represents the inter-vehicle distance between the vehicle and the preceding vehicle, α and β are predetermined coefficients, and n is a predetermined positive real number of 1 or less, and wherein the degraded consciousness determining section is configured to determine that the driver has the degraded consciousness when the calculated likelihood is lower than the calculated likelihood threshold value and to determine that the driver has not the degraded consciousness when the calculated likelihood is equal to or higher than the calculated likelihood threshold value, wherein the calculated likelihood is used as a degree of normal traveling that indicates a normal accelerating operation condition, representing an accelerating operation condition when the driver is in consciousness, and the calculated likelihood threshold value is used as a normal traveling degree threshold value. a proximity condition calculating section that is configured to calculate a proximity to a preceding vehicle positioned in front of the vehicle; an operation condition detecting section that is configured to detect an accelerating operation condition of the driver; a distribution generating section that is configured to generate a distribution of the accelerating operation condition of the driver with respect to the proximity, wherein the distribution indicates a relationship between proximities calculated by the proximity condition calculating section and accelerating operation conditions detected by the operation condition detecting section based on data sampling repeatedly performed over a predetermined time; a likelihood calculating section that is configured to calculate a likelihood, said likelihood indicating a likelihood of the accelerating operation condition of the driver detected by the operation condition detecting section with respect to the proximity calculated by the proximity condition calculating section, and a likelihood threshold value from the distribution generated by the distribution generating section; and a degraded consciousness determining section that is configured to determine whether the driver has the degraded consciousness, wherein the proximity condition calculating section is configured to calculate, as the proximity, an index of perceptual risk estimate, PRE, by the expression PRE=(Vr+α·Vs+β·Ax)/D n, where Vr represents the relative speed of the vehicle with respect to the preceding vehicle, Vs represents the vehicle speed of the vehicle, Ax represents the relative acceleration of the vehicle with respect to the preceding vehicle, D represents the inter-vehicle distance between the vehicle and the preceding vehicle, α and β are predetermined coefficients, and n is a predetermined positive real number of 1 or less, and wherein the degraded consciousness determining section is configured to determine that the driver has the degraded consciousness when the calculated likelihood is lower than the calculated likelihood threshold value and to determine that the driver has not the degraded consciousness when the calculated likelihood is equal to or higher than the calculated likelihood threshold value, wherein the calculated likelihood is used as a degree of normal traveling that indicates a normal accelerating operation condition, representing an accelerating operation condition when the driver is in consciousness, and the calculated likelihood threshold value is used as a normal traveling degree threshold value.