A power tool comprising: a power source including an output shaft which rotates around a thrust shaft; a transmission mechanism including a gear train for changing a rotation speed of the output shaft between a plurality of transmission gear ratios and capable of selecting one of the transmission gear ratios by changing a combination of gears of the gear train to be meshed with each other; a transmission ratio switching operation unit (25; 26) capable of turning around the thrust shaft and operating to change the combination of the gears of the gear train; a holding spring configured to hold an operation position of the transmission ratio switching operation unit (25; 26); a gear operation mechanism (63, 29a, 42c, 46b) configured to move a transmission gear (42; 46) of the gear train in a thrust shaft direction in accordance with turning motion of the transmission ratio switching operation unit (25; 26); and a biasing mechanism (32, 65) configured to bias the gear operation mechanism (63, 29a, 42c, 46b) in accordance with the turning motion of the transmission ratio switching operation unit (25; 26) such that the transmission gear (42; 46) moves in the thrust shaft direction and meshes with a meshed gear corresponding to a selected one of the transmission gear ratios, wherein the power tool is characterized in that the biasing mechanism (32, 65) functions as a turning biasing mechanism configured to engage with the transmission ratio switching operation unit (25; 26) to generate a biasing force around the thrust shaft, and the turning biasing mechanism (32, 65) is configured to bias the gear operation mechanism (63, 29a, 42c, 46b) in the thrust shaft direction by the biasing force acting around the thrust shaft to make the transmission gear (42; 46) mesh with the meshed gear. a power source including an output shaft which rotates around a thrust shaft; a transmission mechanism including a gear train for changing a rotation speed of the output shaft between a plurality of transmission gear ratios and capable of selecting one of the transmission gear ratios by changing a combination of gears of the gear train to be meshed with each other; a transmission ratio switching operation unit (25; 26) capable of turning around the thrust shaft and operating to change the combination of the gears of the gear train; a holding spring configured to hold an operation position of the transmission ratio switching operation unit (25; 26); a gear operation mechanism (63, 29a, 42c, 46b) configured to move a transmission gear (42; 46) of the gear train in a thrust shaft direction in accordance with turning motion of the transmission ratio switching operation unit (25; 26); and a biasing mechanism (32, 65) configured to bias the gear operation mechanism (63, 29a, 42c, 46b) in accordance with the turning motion of the transmission ratio switching operation unit (25; 26) such that the transmission gear (42; 46) moves in the thrust shaft direction and meshes with a meshed gear corresponding to a selected one of the transmission gear ratios, wherein the power tool is characterized in that the biasing mechanism (32, 65) functions as a turning biasing mechanism configured to engage with the transmission ratio switching operation unit (25; 26) to generate a biasing force around the thrust shaft, and the turning biasing mechanism (32, 65) is configured to bias the gear operation mechanism (63, 29a, 42c, 46b) in the thrust shaft direction by the biasing force acting around the thrust shaft to make the transmission gear (42; 46) mesh with the meshed gear.