Reaction apparatus

A reactor comprising:

• a heat exchanging body including therein a heat medium flow channel in which a heat medium fluid is caused to flow, and a reaction flow channel in which a reaction fluid is caused to flow;
• and
• at least one detection part that detects temperature of a fluid flowing in at least one flow channel of the heat medium flow channel and the reaction flow channel,
• wherein the heat exchanging body has:
• at least one installation hole formed to extend in a skew position with respect to the at least one flow channel so as to include an opening portion communicating with the at least one flow channel, in which the at least one detection part is installed at the opening portion so as to be contactable with the fluid flowing in the at least one flow channel;
• and
• at least one fluid guide hole formed along the at least one flow channel from the opening portion of the at least one installation hole.