PROBLEM TO BE SOLVED: To provide a control device enabling a stable work of less amount of variation in the number of revolution to be carried out even under a partial load in a method for operating an internal combustion engine in a manual-operated work machine.SOLUTION: An ignition control device sets at least one ignition time ZZP in regard to each of the number of revolutions. That is, it sets a first ignition time ZZP 1 co-related to each of the number of revolution (n) of a first range 32 of the number of revolutions and a second ignition time ZZP 2 co-related to each of the number of revolutions (n) in a second range 33 of the number of revolutions in interface with the first range (32) of the number of revolution. Each of the first igniting time ZZP 1 is an igniting time ZZP of the first range 49 of the ignition time, each of the second ignition times ZZP 2 is an ignition time ZZP in the second range 50 of the ignition time and each of the first ignition times ZZP 1 is set delay at least only by a crank shaft angle of 5° than that of each of the second ignition times ZZP 2.【課題】作業機における内燃エンジンの作動方法において、部分負荷時にも回転数変動が少ない安定した作動が可能になる制御装置を提供する。【解決手段】点火制御装置は各回転数に対し少なくとも1つの点火時点ZZPを設定する。すなわち第1の回転数範囲32の各回転数nに対し関連付けられる第1の点火時点ZZP1と、前記第1の回転数範囲32に境を接する第2の回転数範囲33の各回転数nに対し関連付けられる第2の点火時点ZZP2とを設定する。各第1の点火時点ZZP1は第1の点火時点範囲49の点火時点ZZPであり、各第2の点火時点ZZP2は第2の点火時点範囲50の点火時点ZZPであり、前記各第1の点火時点ZZP1は少なくとも5゜のクランク軸角度だけ前記各第2の点火時点ZZP2よりも遅く設定されている。【選択図】図4