The magnetic structure of the intermetallic compound EuGa4 was investigated using single-crystal neutron diffraction with the time-of-flight (TOF) Laue technique on the new diffractometer SENJU at the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). Despite of the high neutron absorption of Eu, a vast number of diffraction spots were observed without isotope enrichment. The magnetic reflections appeared at positions with diffraction indices of h + k + l ≠ 2n below 16 K, indicating that the ordering vector is q = (0, 0, 0). The continuous evolution of the magnetic reflection intensity below TN follows a squared Brillouin function for S = 7/2. By adopting a wavelength-dependent absorption collection, the magnetic structure of EuGa4 was revealed that a nearly full magnetic moment of 6.4 μB of Eu lies within the basal plane of the lattice. In this study, we reveal a well-localized divalent Eu magnetism in EuGa4 and demonstrate a high ability of SENJU to investigate materials with high neutron absorption.