A fastener driving tool has a housing, a nose portion, a magazine, a
motor, a plunger, a drive mechanism, a trigger switch, a detection
switch, an energizing switch, a failure detection circuit. The magazine
is configured to store and supply a fastener to the nose portion. The
motor is provided in the housing. The a plunger is provided in the
housing to move between a top dead center and a bottom dead center. The
plunger has a blade for impacting the fastener. The drive mechanism is
configured to drive the plunger with power from the motor. The trigger
switch is configured to drive the drive mechanism, and operated by a
user. The detection switch is configured to be switched according to an
arrangement of the drive mechanism. The energizing switch is configured
to control power feed of the motor. The energizing switch is switched by
the trigger switch and the detection switch. The failure detection
circuit is configured to turn off the energizing switch, based on a
condition of the detection switch prior to impacting the fastener.