A duty ratio control device (100) includes a duty ratio calculation unit (102) and a parameter setting unit (102). The duty ratio calculation unit (102), when an acceleration manipulation is performed, calculates a control duty ratio per predetermined timing based on a value of at least one parameter so that a rotation speed of a motor (22) mounted on an electric power tool (10) reaches a target rotation speed corresponding to the acceleration manipulation. The control duty ratio is calculated to be larger as the value of the at least one parameter is larger. The parameter setting unit (102) sets the value of the at least one parameter. The value of the at least one parameter set for a reacceleration manipulation is larger than the value of the at least one parameter set for an initial acceleration manipulation.
