In an engine igniting coil device comprising an ignition coil assembly potted integrally in a coil case by injecting melted insulating resin, a secondary coil is formed on a coil bobbin by bank winding an element wire in layers of wire turns one over another at a certain bank angle in an axial direction on the bobbin and by slope-winding of layers on the end portion of the bobbin by tapering the coil (by reducing the number of layers therein) in the winding direction. This allows setting a dielectric strength of interlayer insulation of the secondary coil according to the potential distribution therebetween, which is secured by forming an insulation resin layer of a reduced thickness between the coil case and the secondary coil of the secondary coil bobbin, thus realizing the compact engine-igniting coil device.