Inattention determining device

An inattention determining device (10) includes range changing unit (28) and inattention determining unit (27). When a curve detection result is output from curve detector (26), the range changing unit changes a first predetermined range to a second predetermined range by the predetermined amount in the curve direction before a turning direction of an acquisition result from a vehicle state acquiring unit (25) changes the first predetermined range to a second predetermined range. The inattention determining unit determines whether or not a driver is in an inattention state on the basis of the second predetermined range.