A pressure sensor has a Si device having a first main surface that has a bonded area, a second main surface parallel to the first main surface, a pressure-sensitive resistor formed on the first main surface, and a joining assist pattern formed on the first main surface, and a pressing member bonded to the bonded area on the first main surface and compressing the Si device in a thickness direction. The pressure-sensitive resistor has a first bonded section which is placed within the bonded area of the first main surface and is bonded to the pressing member. The joining assist pattern has a second bonded section which is made of the same material as the first bonded section of the pressure-sensitive resistor and is placed within the bonded area of the first main surface and is bonded to the pressing member.