The sealing property obtained when a battery pack is attached to an electric power tool is improved. An electric power tool to/from which a battery pack retaining a battery cell is attachable/detachable has: a tool main body being provided with an attachment part to/from which the battery pack is attached/detached; a guide groove which is provided in the attachment part and which determines a direction of the attachment/detachment of the battery pack; a device-side terminal which is provided in the attachment part and which is connected to a battery-side terminal provided in the battery pack; and a seal member which is provided in the attachment part and which seals a connecting part between the battery-side terminal and the device-side terminal.