Rice is typically a short-day plant and possesses a complex genetic regulation for determining the heading date. Rice Heading date 3a (Hd3a) and Rice FT-like 1 (RFT1) florigen genes mainly regulate its flowering trait. Gemdjah Beton (GB) is an Indonesian native rice cultivar under the ecotype Bulu. We selected early-heading plants in M1 population generated by carbon-ion irradiation to dry seeds of GB. Among them, there was only one line that exhibited early-heading phenotype in both M2 and M3 generations. We isolated fixed mutant with early-heading from M3 generation, designated this mutant line as GBM10, and used it as plant material. GBM10 flowered approximately 17 days earlier than wild-type (WT) under Long-day (LD) conditions. However, the heading dates between GBM10 and WT showed no clear difference under Short-day (SD) conditions. A Real-time quantitative RT-PCR was performed to check the gene expression of two florigen genes, Hd3a and RFT1. Those florigen expressions were clearly induced under LD conditions in GBM10 compared to WT. Under SD conditions there was no significant difference in their relative expression. This florigen expression agrees with the heading-date phenotypes. We performed MutMap analysis using BC1F4 generation and found that a single nucleotide variant (SNV) that occurred on chromosome seven was genetically linked to the early heading phenotype of GBM10 lines. Further linkage analysis showed that the pattern of the inheritance of the early heading phenotype was semi-dominant. Based on these results, we reported the successful isolation of GBM10 as an early heading mutant.