A method of manufacturing a semiconductor device includes forming a thin film containing a specific element, oxygen, carbon, and nitrogen by performing a cycle a predetermined number of times. The cycle includes supplying a specific element-containing gas, supplying a carbon-containing gas, supplying an oxidizing gas, and supplying a nitriding gas. The act of supplying the nitriding gas is performed before the act of supplying the specific element-containing gas, and the act of supplying the carbon-containing gas and the act of supplying the oxidizing gas are not performed until the act of supplying the specific element-containing gas is performed.