Document And Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2021	Dec. 16, 2021	Mar. 31, 2021
Document And Entity Information
Document Type	10-K
Amendment Flag	false
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity File Number	000-54986
Entity Incorporation, State or Country Code	NV
Entity Registrant Name	Arch Therapeutics, Inc.
Entity Tax Identification Number	46-0524102
Entity Address, Address Line One	235 Walnut Street
Entity Address, Address Line Two	Suite 6
Entity Address, City or Town	Framingham
Entity Address, Country	MA
Entity Address, Postal Zip Code	01702
City Area Code	617
Local Phone Number	431-2313
Title of 12(g) Security	Common Stock, par value $0.001 per share
Entity Central Index Key	0001537561
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Public Float			$ 32,000,000
Trading Symbol	ARTH
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		237,169,770