| Document And Entity Information | Feb. 23, 2023 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 23, 2023 |
| Entity Registrant Name | Apexigen, Inc. |
| Entity Central Index Key | 0001814140 |
| Entity Emerging Growth Company | true |
| Securities Act File Number | 001-39488 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 85-1260244 |
| Entity Address, Address Line One | 75 Shoreway Road |
| Entity Address, Address Line Two | Suite C |
| Entity Address, City or Town | San Carlos |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94070 |
| City Area Code | (650) |
| Local Phone Number | 931-6236 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Ex Transition Period | false |
| Warrants Each Whole Warrant Exercisable For One Share Of Common Stock At An Exercise Price Of 11.50 Per Share [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Warrants, each whole warrant exercisable for one share of Common Stock at an exercise price of $11.50 per share |
| Trading Symbol | APGNW |
| Security Exchange Name | NASDAQ |
| Common Stock 0.0001 Par Value Per Share [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock, $0.0001 par value per share |
| Trading Symbol | APGN |
| Security Exchange Name | NASDAQ |
