A substrate processing apparatus includes: a processing vessel configured to be vacuumed; a holding unit configured to hold a plurality of substrates and to be inserted into or separated from the processing vessel; a gas supply unit configured to supply gas into the processing vessel; a plasma generation box partitioned and formed by a plasma partition wall; an inductively coupled electrode located at an outer sidewall of the plasma generation box along its length direction; a high frequency power supply connected to the inductively coupled electrode through a feed line; and a ground electrode located outside the plasma generation box and between the processing vessel and the inductively coupled electrode and arranged in the vicinity of the outer sidewall of the plasma generation box or at least partially in contact with the outer sidewall.