A load detection device for a vehicle seat mounted between a floor side mounting mechanism and a seat side mounting mechanism and measuring a load applied by an occupant seated on the vehicle seat, includes a shaft member adapted to be fixed to one of the floor side mounting mechanism and the seat side mounting mechanism, a strain generating member fixed to the shaft member and including a hole into which the shaft member is press-fitted, a strain gauge attached to the strain generating member, the shaft member of which surface hardness is specified to be lower than a surface hardness of the hole and including a scraping projecting portion scraped off by means of the hole in a case where the shaft member is press-fitted to the hole, and an inter space formed between the strain generating member and the shaft member and positioned next to the scraping projecting portion.