A power tool includes a power source, a speed change mechanism and a tool bit. The speed change mechanism includes first and second rotating shafts disposed parallel to each other, a first power transmission path provided with a first gear train and a first clutch and a second power transmission path provided with a second gear train and a second clutch. The power transmission path is switched between the first power transmission path and the second power transmission path while the first and second gear trains are held engaged, by shifting of the first and second clutches between the power transmission state and the power transmission interrupted state according to a load applied to the tool bit. The speed change mechanism further includes a switching retaining mechanism, a switching preventing mechanism, a switching set value adjusting mechanism or a switching mechanism.