An accessory device mountable to an accessory shoe of an image-pickup apparatus includes a contact member electrically connecting with the accessory shoe, a lock mechanism allowing a lock operation for fixing the accessory device to the accessory shoe and an unlock operation for releasing the fix of the accessory device, a drip-proof member contacting the image-pickup apparatus to form a drip-proof space around the contact member and the accessory shoe. In response to the lock operation, the drip-proof member is moved to a first position where the drip-proof member is allowed to be brought into contact with the image-pickup apparatus. In response to the unlock operation, the drip-proof member is moved to a second position where the drip-proof member is retracted from the first position. The drip-proof member has a shape such that a length of a rear-end-side portion is longer than that of the front-end-side portion.