Provided are a chainsaw and a handheld power tool. The handheld power tool includes a motor; a handle, where a first switch that can control the starting and stopping of the motor is disposed on the handle; an output assembly; and an adjustment device including a telescopic rod assembly, where the length of the adjustment device changes so that the handheld power tool has at least two working states, that is, a first working state and a second working state. The distance between the frontmost side of the handheld power tool and the rearmost side of the first switch is defined as the effective length of the handheld power tool; where when the handheld power tool is in the first working state, the handheld power tool has a first effective length T1; and when the handheld power tool is in the second working state, the handheld power tool has a second effective length T2; where the first effective length T1 is less than or equal to 1 m, and the second effective length T2 is greater than the first effective length T1. The chainsaw and the handheld power tool are convenient, lightweight, and flexible while satisfying the requirements of the user for different trimming heights.