An engine control device for a tractor, the tractor comprising: a mode selection device configured to switch between a standard engine performance curve to obtain predetermined output and a fuel efficient engine performance curve to reduce fuel consumption in comparison to the standard engine performance curve; and an engine speed maintenance control mode in which when load is applied, an engine speed is maintained at a preset speed, and an engine speed change control mode in which when load is applied, the engine speed is controlled to decrease according to the load, and wherein the engine control device is configured to control the tractor such that automatic switching to the engine speed maintenance control mode is performed when the standard engine performance curve is selected by the mode selection device and a PTO drive switch which drives an implement attached to the tractor is turned on, and when a determination is made that there is a margin in engine load, the fuel efficient engine performance curve is selected by the mode selection device and automatic switching to the engine speed change control mode is performed, and wherein the engine control device is configured to control the tractor such that automatic switching to the engine speed change control mode is performed when the fuel efficient engine performance curve is selected by the mode selection device and the PTO drive switch which drives the implement is turned on, and when a determination is made that there is no margin in the engine load, the standard engine performance curve is selected by the mode selection device and automatic switching to the engine speed maintenance control mode is performed, and wherein the engine control device is configured to control the tractor such that switching to the engine speed maintenance control mode is performed in a case that a lift arm that connects the implement may be raised and lowered while the lift arm is located lower than an uppermost position of the lift arm even when the PTO drive switch is turned off. a mode selection device configured to switch between a standard engine performance curve to obtain predetermined output and a fuel efficient engine performance curve to reduce fuel consumption in comparison to the standard engine performance curve; and an engine speed maintenance control mode in which when load is applied, an engine speed is maintained at a preset speed, and an engine speed change control mode in which when load is applied, the engine speed is controlled to decrease according to the load, and wherein the engine control device is configured to control the tractor such that automatic switching to the engine speed maintenance control mode is performed when the standard engine performance curve is selected by the mode selection device and a PTO drive switch which drives an implement attached to the tractor is turned on, and when a determination is made that there is a margin in engine load, the fuel efficient engine performance curve is selected by the mode selection device and automatic switching to the engine speed change control mode is performed, and wherein the engine control device is configured to control the tractor such that automatic switching to the engine speed change control mode is performed when the fuel efficient engine performance curve is selected by the mode selection device and the PTO drive switch which drives the implement is turned on, and when a determination is made that there is no margin in the engine load, the standard engine performance curve is selected by the mode selection device and automatic switching to the engine speed maintenance control mode is performed, and wherein the engine control device is configured to control the tractor such that switching to the engine speed maintenance control mode is performed in a case that a lift arm that connects the implement may be raised and lowered while the lift arm is located lower than an uppermost position of the lift arm even when the PTO drive switch is turned off.