A particulate sensor (1) which detects particulates S contained in a gas under measurement (EG) flowing within a gas flow pipe (EP) has a space forming portion (12) and an ion source (15). The space forming portion (12) projects into the gas flow pipe EP and forms an internal space MX. The space forming portion (12) has an introduction port (43I) and a discharge port (48O) for discharging from the internal space MX the gas EGI introduced through the introduction port (43I). The source (15) produces ions CP by gaseous discharge. The space forming portion (12) is configured such that the introduced gas EGI is discharged from the internal space MX through the discharge port (48O), the gas under measurement EG is introduced into the internal space MX through the introduction port (43I), and the introduced gas EGI is mixed with the ions CP produced by the ion source (15).