An unequal interval combustion engine misfire determination device that is configured to determine a misfire in an unequal interval combustion engine including a plurality of cylinders in which combustion occurs at unequal intervals and a crankshaft , wherein in the unequal interval combustion engine , an interval between a crank angle where one cylinder causes combustion and a crank angle where another cylinder next to the one cylinder causes combustion varies depending on cylinders , the determination being performed based on a crank angle signal indicating a rotation angle of the crankshaft , the unequal interval combustion engine misfire determination device comprising: an acquisition unit that is configured to acquire a fluctuation canceled value (NEOMG), in which a fluctuation component attributable to unequal interval combustion is canceled, for every 720 crank angle degrees based on the crank angle signal while the unequal interval combustion engine is in operation, wherein the acquisition unit is configured to acquire the fluctuation canceled value (NEOMG) as a rotation speed in a section of 720×m crank angle degrees including a predetermined determination angle position (t2, t3), where m is a natural number; a calculation unit that is configured to calculate a fluctuation manifested value (AOMG), in which the fluctuation component attributable to unequal interval combustion is manifested, based on the crank angle signal while the unequal interval combustion engine is in operation, the calculation being performed by removing, from a rotation speed (OMG) at the determination angle position (t2, t3), the fluctuation canceled value (NEOMG) acquired by the acquisition unit and being a rotation speed in a section of 720xm crank angle degrees including the determination angle position (t2, t3); and a determination unit that is configured to determine a misfire in a specific cylinder among the plurality of cylinders included in the unequal interval combustion engine , based on the fluctuation manifested value (AOMG) calculated by the calculation unit while the unequal interval combustion engine is in operation, and a predetermined reference value prestored in the misfire determination device . an acquisition unit that is configured to acquire a fluctuation canceled value (NEOMG), in which a fluctuation component attributable to unequal interval combustion is canceled, for every 720 crank angle degrees based on the crank angle signal while the unequal interval combustion engine is in operation, wherein the acquisition unit is configured to acquire the fluctuation canceled value (NEOMG) as a rotation speed in a section of 720×m crank angle degrees including a predetermined determination angle position (t2, t3), where m is a natural number; a calculation unit that is configured to calculate a fluctuation manifested value (AOMG), in which the fluctuation component attributable to unequal interval combustion is manifested, based on the crank angle signal while the unequal interval combustion engine is in operation, the calculation being performed by removing, from a rotation speed (OMG) at the determination angle position (t2, t3), the fluctuation canceled value (NEOMG) acquired by the acquisition unit and being a rotation speed in a section of 720xm crank angle degrees including the determination angle position (t2, t3); and a determination unit that is configured to determine a misfire in a specific cylinder among the plurality of cylinders included in the unequal interval combustion engine , based on the fluctuation manifested value (AOMG) calculated by the calculation unit while the unequal interval combustion engine is in operation, and a predetermined reference value prestored in the misfire determination device . <EOS>