An inkjet printer comprising: an inkjet head configured to discharge ink droplets from nozzles formed in an ink discharging surface thereof; a head moving unit configured to reciprocate the inkjet head relative to a recording sheet along a head moving direction parallel to the ink discharging surface; a wave shape generating mechanism (15, 18, 19) configured to deform the recording sheet in a predetermined wave shape that has top portions of portions protruding in a first direction toward the ink discharging surface and bottom portions of portions recessed in a second direction opposite to the first direction, the top portions and the bottom portions alternately arranged along the head moving direction; and a storing unit configured to store gap information related to a gap between the ink discharging surface and the recording sheet, the gap information comprising a plurality of pieces of gap information respectively corresponding to a plurality of examined sections discretely arranged along the head moving direction on the recording sheet, each of the plurality of examined sections including a corresponding one portion of the top portions and the bottom portions on the recording sheet; characterized by: a calculating unit configured to calculate interpolation gap information to be interpolated over a whole width in the head moving direction of at least one of a plurality of segments, each of which has a width in the head moving direction defined by two adjacent sections of the plurality of examined sections, based on the gap information stored in the storing unit. an inkjet head configured to discharge ink droplets from nozzles formed in an ink discharging surface thereof; a head moving unit configured to reciprocate the inkjet head relative to a recording sheet along a head moving direction parallel to the ink discharging surface; a wave shape generating mechanism (15, 18, 19) configured to deform the recording sheet in a predetermined wave shape that has top portions of portions protruding in a first direction toward the ink discharging surface and bottom portions of portions recessed in a second direction opposite to the first direction, the top portions and the bottom portions alternately arranged along the head moving direction; and a storing unit configured to store gap information related to a gap between the ink discharging surface and the recording sheet, the gap information comprising a plurality of pieces of gap information respectively corresponding to a plurality of examined sections discretely arranged along the head moving direction on the recording sheet, each of the plurality of examined sections including a corresponding one portion of the top portions and the bottom portions on the recording sheet; characterized by: a calculating unit configured to calculate interpolation gap information to be interpolated over a whole width in the head moving direction of at least one of a plurality of segments, each of which has a width in the head moving direction defined by two adjacent sections of the plurality of examined sections, based on the gap information stored in the storing unit. a calculating unit configured to calculate interpolation gap information to be interpolated over a whole width in the head moving direction of at least one of a plurality of segments, each of which has a width in the head moving direction defined by two adjacent sections of the plurality of examined sections, based on the gap information stored in the storing unit.