A driver condition determination device determines whether a driver of a host vehicle has degraded consciousness. A main component for distribution of an accelerating operation condition with respect to proximity when tailgating a preceding vehicle is analyzed (S 16), all data is origin-shifted (S18), and the accelerating operation condition of the driver when the driver has consciousness is created as a normal traveling model (S20). The likelihood of the accelerating operation condition, a likelihood average, a likelihood variance, and a likelihood threshold value are calculated (S22 to S26), and it is determined whether the likelihood of a current driving operation is lower than the likelihood threshold value (S28). When the likelihood is lower than the likelihood threshold value, the driver is determined as being in degraded consciousness. Since the likelihood threshold value is calculated for determination on the basis of data when the driver has consciousness, an erroneous determination of degraded consciousness due to difference in driver operation characteristics is suppressed.