A spindle locking device for a portable machine tool includes a locking unit and a movement activation unit. The locking unit has a movably mounted locking element configured to lock a spindle of the portable machine tool in at least one direction, and an operating element configured to actuate the locking element. The movement activation unit is configured to pretension the locking element in a direction towards a locking position, at least when the operating element is in an unactuated position.