To provide a wiper device easily and surely implementing an antitheft countermeasure of a car.

A rear window wiper device 10 comprises: a wiper motor 11 attached to the inside of an open/close body 1 of a vehicle body; a pivot shaft 14 driven by the wiper motor, supported by a shaft support part 12a, and having a tip projected from the open/close body 1 of the vehicle body 1 to the outside; a wiper arm 16 attached to the pivot shaft and wiping a rear window glass 2; and an antitheft cap 20 interposed between the shaft support part 12a and the open/close body 1. The cap 20 includes: a cylindrical body part 21 made from synthetic resin and fitted to the cylindrical shaft support part 12a; and a covering part 24 extended upward from the body part and covering an opening 2a of the open/close body 1. Ribs 22 and projections 23b are alternately arranged on an inner circumferential face of the cylindrical body part 21 so that the ribs 22 and the projections 23b are vertically separated from each other.