A mass spectrometer includes: an ionization unit configured to ionize an analyte gas; a filter unit configured to allow passage of only a target ion which is a component of the analyte gas ionized in the ionization unit and which has a specific mass-to-charge ratio; and an ion detection unit configured to detect an ion detection value based on the target ion having passed through the filter unit, wherein the ion detection unit includes a Faraday electrode which includes an electrode portion disposed along a centerline of the filter unit and a bottom electrode provided at a position downstream of the electrode portion in a flow of the target ion, the electrode portion and the bottom electrode being connected to each other, a secondary electron multiplier provided to face the electrode portion with the centerline located therebetween, and a blocking portion connected to the bottom electrode.