A pyroelectric detector includes a pyroelectric detection element, a support member, and a support part. The pyroelectric detection element has a capacitor including a first electrode, a second electrode, and a pyroelectric body disposed between the first and second electrodes, and a first reducing gas barrier layer that protects the capacitor from reducing gas. The support member includes first and second sides with the pyroelectric detection element being mounted on the first side and the second side facing a cavity. The support member has a mounting member on which the capacitor is mounted and an arm member linked to the mounting member. The support part supports a portion of the support member. An outer peripheral edge of the first reducing gas barrier layer is disposed between and spaced apart from an outer peripheral edge of the mounting member and an outer peripheral edge of the capacitor in plan view.